Definition of filter in English:



  • 1A porous device for removing impurities or solid particles from a liquid or gas passed through it:

    ‘an oil filter’
    • ‘We had travelled the rough un-surfaced, ungraded roads for nearly a fortnight without mishap, but now sand had clogged the filter and the vehicle coughed to a halt.’
    • ‘The pump has a filter to remove all the harmful bacteria.’
    • ‘He said buses were already being fitted with special filters to remove and ‘burn off’ particulates.’
    • ‘After passing through a filter, the oil and fuel mixture is put into the vehicle's fuel tank to be burned as fuel.’
    • ‘The filter removes pollen and dust that is brought in from the outside through the heating and cooling system.’
    • ‘There are no air filters, oil filters or other diesel waste material.’
    • ‘And you have to run the car to make the oil hot before you drain the oil and take the filter off.’
    • ‘We collected wastewater from the kitchen in a house and obtained pure water after passing it through the filter.’
    • ‘Electronic air cleaners are 10 to 20 times more efficient than standard filters.’
    • ‘The former removed the filter and blew it clear while the latter stood guard.’
    • ‘Because the filter stops allergens from entering your body it prevents them triggering hay fever.’
    • ‘The ground is an excellent filter for removing bacterial and other contamination.’
    • ‘Several cancer causing chemical compounds that are created in the presence of disinfectants are also stopped by the filter.’
    • ‘When the tool is removed from the well, it will carry the suspended particles with it, trapped by the filter, thus removing them from the well fluid.’
    • ‘Sunday morning one weekend, I was searching for coffee filters through the kitchen cupboards.’
    • ‘These filters usually trap large particles of sand, dirt or mineral contaminants and treat all of the water used in the house.’
    • ‘Despite manufacturer claims, ozone filters don't remove particles from the air, including those that cause most allergies.’
    • ‘When you slide the front section out and unscrew the front, you can see that the intake fan has two removable dust filters to help stop dust being sucked into your case.’
    • ‘As crews throughout the province move in to harvest and mill the black wood, the immediate problem is carbon: it clogs filters, shorts out electrical circuits, and dulls saws.’
    • ‘Even the dissolved salts don't get through these reverse osmosis filters.’
    strainer, sifter
    sieve, riddle, colander
    gauze, netting
    View synonyms
    1. 1.1 A filter tip:
      [as modifier] ‘a cheap filter cigarette’
      • ‘Cigarette filters, which can last up to 100 years - are designed to absorb tar and other chemicals from the cigarette.’
      • ‘She breathed in my ear, sipping her coffee and smoking one of those cigarettes with the big filters.’
      • ‘The material was sprayed onto buildings, used in shipyards, it covered pipes, was weaved into cloth and was even placed in cigarette filters.’
      • ‘And the problem was he was smoking those terrible cigarettes without filters.’
      • ‘You'd think that not having to add a filter would make the cigarette cheaper, but that doesn't seem to be the case.’
      • ‘It would almost be like smokers 50 years ago trying to get tobacco companies to pay to put filters on all cigarettes, just in case the products turned out to be dangerous.’
      • ‘Dougal took his final drag and stared at the cigarette filter for a few seconds before tossing it over the railing, down to the earth below.’
      • ‘The company, which makes products as diverse as plastic caps and cigarette filters to food packing and carrier bags, is expected to post in-line figures.’
      • ‘Therefore, inhaled tobacco smoke without a filter contains as much as four times more nicotine as a regular filtered cigarette.’
      • ‘According to experts in the field of industrial deafness, the current methods of hearing protection such as ear muffs and plugs are about as effective as filters on cigarettes.’
      • ‘She broke the filter off her cigarette then licked and split it down the paper join.’
      • ‘The cigarette has a filter that makes them harder to inhale, aimed at reducing tar and nicotine consumption.’
      • ‘This been accomplished by the use of filters and filter ventilation, modified cigarette paper and modified forms of tobacco and tobacco blends.’
      • ‘The filters attach to cigarettes and gradually reduce the amount of nicotine consumed.’
      • ‘This involved tearing off the filter portion of each cigarette and heaping them on a non-stick oven sheet.’
      • ‘US studies have suggested that the shift of longstanding smokers to low tar filter cigarettes results in the smoker inhaling more deeply and retaining smoke longer.’
      • ‘The air possessed a pungent, acrid smell because the cigarette had burned through a filter stub in the overflowing ashtray.’
      • ‘Like, twenty plastic bags filled with those cigarette filters.’
      • ‘This will bring the price of a standard pack of filter cigarettes to 4.15.’
      • ‘The company also makes cigarette filters, ink reservoirs and self-adhesive tear tapes.’
    2. 1.2 A screen, plate, or layer of a substance which absorbs light or other radiation or selectively absorbs some of its components:
      ‘filters can be used in photography to reduce haze’
      • ‘If you must shoot with it, you can use a light pink FLD filter with daylight films to remove some of the greenish cast.’
      • ‘Cinematography is the technical craft of shooting a film: the camera, lens, film, filters, framing, etc.’
      • ‘However, many species then alter the spectra of the emitted light using spectral filters and reflectors.’
      • ‘Digital cameras can also mount filters, auxiliary lenses and polarizers allowing you to meet any photographic challenge you might come across with.’
      • ‘Soft-focus or diffusion filters give a misty quality to images and can impart a romantic mood to scenics and flower close-ups.’
      • ‘The anti-alias filter sits between the lens and the mirror and can be removed if required by removing a two small screws.’
      • ‘In the eleventh century he did not have the advantage of either a telescope to project an image safely onto a screen or optical filters.’
      • ‘Without their UV-blocking filters, quartz halogen lamps were observed to emit wavelengths even shorter than 250 nm.’
      • ‘I have tried to get these bright and vibrant colors with a polarizer filter but the colors were not enough.’
      • ‘You can use this haze to advantage, but if it is obscuring your subject, you may need to place a filter over your SLR lens.’
      • ‘To cut down on the glare, he used a polarized filter on his camera.’
      • ‘This opening was then covered with one to six layers of neutral-density filters made from a sheet of developed X-ray film.’
      • ‘But there are more varieties of soft focus filters than there are adjectives describing them.’
      • ‘A wavelength range between 350 and 800 nm was selected by optical filters.’
      • ‘The vain portrait sitter certainly won't mind if a wrinkle or two is removed by the use of a soft focus filter of a bit of silk in front of the lens.’
      • ‘Sony's trick is to apply an anti-glare filter to the screen that doesn't scatter light the way other filters do.’
      • ‘As a serious photography project, this is one time you do not need wide angle lenses, special filters or off camera flash guns.’
      • ‘Thinking that his telescope or filter was allowing light to leak into the projected image, he adjusted his instrument.’
      • ‘The beam output was not lowered because it burned through the neutral density filters.’
      • ‘A screen on the light box filters out ultraviolet rays.’
      sieve, riddle, sifter, strainer, colander, filter, winnow
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    3. 1.3 A device for suppressing electrical or sound waves of frequencies not required.
      • ‘Rectifiers and trap filters are strongly recommended on all variable frequency drives.’
      • ‘The second image-analysis method uses a 2-D frequency band-reject filter.’
      • ‘The input signal must be of a specific frequency to be conducted through the filters and of specific amplitude to overcome the offset.’
      • ‘Many digital speaker processors, which are often used primarily as crossovers, also include filters for frequency correction.’
      • ‘If one of the two obviously is higher than the other, adjust the related frequency filters as needed.’
      • ‘Passive components are capacitors, resistors, connectors, filters, inductors, and oscillators.’
      • ‘Crosstalk from synchronizing signals is suppressed by filters.’
      • ‘We did this by assessing the performance of both filters in filtering noise signals obtained from both habitats throughout the breeding season.’
      • ‘Only very high-end receivers will provide the filters for all signals.’
      • ‘The extremely narrow lines of the solar spectrum require filters with correspondingly high resolution.’
      • ‘The digital filter operated in the frequency domain employing an inverse Fourier algorithm.’
      • ‘However, replacing the analog filter with a digital filter requires a very precise converter.’
      • ‘Product groups include passive and electromechanical components, capacitors, resistive products, ferrites, fuses, inductors and filters.’
      • ‘A second bandpass filter with a center frequency above the fundamental can be used as the pulse generator.’
      • ‘The screen print in Figure 10 shows the swept frequency response of the low-pass filter.’
      • ‘Finally, consider the wavelengths that are attenuated by the filter.’
      • ‘I could go hotter, but the filters in ADCs require 1 to 2 dB of headroom and you may want your mastering engineer to have some room to work, too.’
      • ‘The filter's feedback implementation compensates for strapdown navigation error and sensor errors.’
      • ‘A spectral analysis of this summed pattern is next performed by a set of bandpass spatial frequency filters.’
      • ‘An electronic filter prevents frequencies from reaching the speakers that are not supposed to receive them.’
    4. 1.4Computing (in image-editing software) a function used to alter the overall appearance of an image in a specific manner:
      ‘many other apps also offer filters for enhancing photos’
    5. 1.5Computing A piece of software that processes data before passing it to another application, for example to reformat characters or to remove unwanted types of material.
      • ‘Most search engines have duplication filters in effect that look past formatting changes and do a very good job of detecting duplicate content.’
      • ‘That will speed up download times and should allow software filters to be reinstalled, to the relief of teachers and parents.’
      • ‘Mr Porter said such filters had been removed because they slowed down access to the Internet.’
      • ‘While half the respondents have Internet access, only a third use software filters to block racy or undesirable Web sites.’
      • ‘Requiring filters would have just made people even less likely to keep an eye on what people on those computers were doing - and could also block out perfectly legitimate sites.’
  • 2British An arrangement whereby vehicles may turn left (or right) while other traffic waiting to go straight ahead or turn right (or left) is stopped by a red light:

    [as modifier] ‘a filter lane’
    • ‘Looking at the points he lists I agree that there should be a visible, designated taxi rank at the top of town and his comments regarding roundabouts, traffic lights and filter lanes are well founded.’
    • ‘In another country I know well an inexpensive and very efficient system is to use a filter which enables traffic to keep on the move and cuts down on frustration and exhaust fumes which here are pretty bad.’
    • ‘Then you think about those people on the roads who selfishly block junctions, who cut you up at a roundabout, who use filter lanes to queue jump.’
    • ‘Other drivers have shown me of their mastery of the finer computer games by their willingness to travel at speeds outside of the law and by the use of filter lanes to avoid stopping.’
    • ‘A filter lane is in place for all cars approaching from the M61 direction.’
    • ‘The Pontiac was travelling north along Bonnet Creek Road in the left-hand filter lane while the Ford van was travelling south on the inside lane, according to police in Florida.’
    1. 2.1 A traffic light signalling a filter arrangement.
      • ‘Several traders suggested introducing a green filter at the traffic lights in Cricklade Road to allow cars to turn right easier.’
      • ‘Then, curiously, a leftturn filter arrow was installed at the traffic lights, replacing a ‘yield’ sign.’
      • ‘Good news for motorists - a filter light for traffic existing from Athy Road on to the Main Street is also in the pipeline.’
      • ‘In it I was assured that plans were in hand to install a right-turn filter once necessary ducting work had been completed.’
      • ‘Why do so many traffic lights not have right turn filters, and why does the filter at Over Hulton never work?’


  • 1[with object] Pass (a liquid, gas, light, or sound) through a device to remove unwanted material:

    ‘the eye filters out ultraviolet radiation’
    • ‘Look for cars with rear-view mirrors that automatically dim and filter out headlight glare.’
    • ‘If you are trying to stop contaminated air being breathed in, you not only have to filter the air, but ensure a good seal between the respirator and the face.’
    • ‘Elevated on columns, these suspended screens filter light and mark out where to walk and where to rest by creating shaded zones and paths.’
    • ‘The new one is lighter, can filter unnecessary noise, and is more durable.’
    • ‘The new mouse adapter filters out the shaking movements of the hand - in a similar way to how the image stabilizing systems of some camera lenses work.’
    • ‘We have been given a special machine for our living room which filters pure oxygen into his lungs.’
    • ‘However, the device was really intended to filter the water in an effort to promote absinthe drinking as hygienic.’
    • ‘And it isn't all filtered through a partisan lens.’
    • ‘An X-ray telescope filters out all the light from the Sun except X rays, and what is left is mostly the solar corona.’
    • ‘The water was then filtered using a white cloth and stored in airtight pots in dark rooms.’
    • ‘Fish sauce is what you get when you leave anchovies or similar small fish to pickle in brine until nearly dissolved, and then filter the resulting liquid.’
    • ‘The expensive equipment filters out toxins from incinerated mercury and cuts the dangerous discharge by 50 per cent.’
    • ‘This layer surrounds the earth and filters ultraviolet light from the rays of the sun.’
    • ‘The alternative is to give official bodies the power to filter what we see and hear.’
    • ‘They enjoyed the event on laptop screen and through a special solar telescope that filters red light emitted by hydrogen in the sun.’
    • ‘The spirit is aged in charred, American oak barrels and then filtered to remove all trace of color.’
    • ‘The water vapor is filtered to remove any remaining brine, then condensed and stored.’
    • ‘His ears filtered the sounds around him, alerting his mind only when a familiar sound crossed his path.’
    • ‘It is a proven fact that the ozone layer filters out much of the harmful radiation from the sun.’
    • ‘The land is mostly peat on a bed of sand, which filters the water.’
    sieve, strain, sift, filtrate, riddle
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    1. 1.1 Process or assess (items) in order to reject those that are unwanted:
      ‘you'll be put through to a secretary whose job it is to filter calls’
      ‘the brain has the ability to filter out information it considers non-essential’
    2. 1.2Computing Process or treat with a filter.
      • ‘It they're in my way then search engines should filter them.’
      • ‘Some of you said we're overplaying the privacy concerns involved in trusting ISPs or managed services providers to filter malicious messages from email traffic.’
      • ‘There's really no good reason to get caught out: simply filtering executable attachments from emails will guard against this virus.’
      • ‘Of course, users may be tempted to filter all server error messages, but that's not a reliable solution because doing so would also block legitimate mail server error messages.’
      • ‘Alas, search engines have always filtered by structure, rather than the message, and so they should.’
  • 2[no object, with adverbial of direction] Move slowly in a specified direction:

    ‘the players filtered out on to the pitch’
    • ‘The strong form remains dominantly there, yet the glass walls allow the public to filter through, to wait and meet, to buy tickets and catalogues.’
    • ‘What is wrong with each driver allowing another motorist to filter into the traffic stream ahead of them where traffic flows need to merge, either at roadworks or at normal junctions?’
    • ‘Then the band members began filtering back into the room, looking disgruntled and disheveled.’
    • ‘The autumn/winter collection at Lakeland is slowly filtering into their stores.’
    • ‘With the equipment slowly filtering into the distribution system, Sprint also seems to be putting early services packages in line.’
    • ‘There was only one door and we all slowly filtered into the crowded band room.’
    • ‘Or how it filters down to the players and becomes the chemistry that fuels champions.’
    • ‘They use melted snow from the mountain range that filters into underground channels.’
    • ‘It filters down through our players to the public through the press.’
    • ‘The family filtered through into an antechamber and the friends passed by us all one at a time, saying their piece.’
    • ‘At least some of the money funnelled into Scottish Enterprise by the politicians actually seems to filter down to the people at the bottom.’
    • ‘The journey home on two hours sleep doesn't bear mention, all the traffic that had filtered into Cornwall over the previous week or two suddenly seemed to leave at once.’
    • ‘Haley can occupy two blockers, allowing linebackers to filter from behind to make plays.’
    • ‘At least an academy has been established, and young players are filtering upwards from it.’
    seep, percolate, leak, trickle, ooze, dribble, bleed, flow
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    1. 2.1 (of light or sound) enter a place slowly or in small quantities:
      ‘sunlight filtered in through the thin curtains’
      • ‘Ryan's door was still shut, though there was some light filtering under his door.’
      • ‘As the sunshine filtered in, a new light came to her face and she sat in all her glory.’
      • ‘As the morning passed, and the sun rose higher in the sky, dappled rays of sunlight filtered through the dense canopy of the jungle, creating dancing patterns on the floor.’
      • ‘Sunlight filtered down through the canopy, falling warmly on her face as she walked beneath the trees.’
      • ‘I had a feeling as the first light filtered through the elms across the road that it might be a pleasant morning.’
      • ‘Light was filtering in through the dusty windows, as impossible as it seemed.’
      • ‘Removing the glass from my lips, I looked over at the kitchen window which was gently filtering the moonlight from outside: the only source of light in the room.’
      • ‘Just then a loud crackling came over the speakers followed by the loud beating of a drum as the heavy rock music slowly filtered out into the car.’
      • ‘He tried hard not to look like a fox, and gazed nonchalantly up to where brief rays of sunlight filtered through the branches of nearby oak trees and onto the decayed husks of dead bluebells.’
      • ‘Yesterday morning was beautiful, the sky was bright blue, it was warm and the sounds filtering into our home were happy.’
      • ‘Bright sunlight filtered down through the trees in patches.’
      • ‘With a sigh she looked up, propping her head on one hand and watching dust motes dance in the rays of sunlight filtering down from above.’
      • ‘Only faint rays of sunlight filtered through the thick leaves overhead.’
      • ‘The only light that filtered into the room came from two windows to her left.’
      • ‘The drawn curtains filtered the faint light with a slight red glow.’
      • ‘Their voices filter through the branches like dust.’
      • ‘Little rays of sunlight filtered through the curtains that were changed overnight.’
      • ‘The metal roofing was added to the structure in 1894, and there is a hole under the dome to allow the sun to filter in.’
      • ‘I felt exhausted and the moonlight slowly filtering through the window and covering everything only reinforced that.’
      • ‘From the window filtered the first lights of the morning and hours had passed.’
      seep, percolate, leak, trickle, ooze, dribble, bleed, flow
      View synonyms
    2. 2.2 (of information) gradually become known:
      ‘the news began to filter in from the hospital’
      • ‘News filtered through that the march had been cancelled after the skirmishes in Stirling.’
      • ‘She was in Portsmouth when news filtered through that the war in Europe was over.’
      • ‘But as the news filtered out, the presidential palace began to be inundated with phone calls expressing disquiet.’
      • ‘I feel sure that many of our senior readers will recall where they were on that very sad Sunday evening as news of death filtered through.’
      • ‘The critical demolition of it filtered into popular consciousness and it became the archetypal bad film.’
      • ‘Slowly it filtered out that they not doing very well and had sustained casualties.’
      • ‘‘The more information filtering through to the workplace the better off we are all going to be,’ Brem says.’
      • ‘An open management style will encourage communication and allow ideas to filter through from all levels of the organisation.’
      • ‘News of the move has filtered through the Northern Ireland political system as the British government has briefed local parties on developments as they unfold.’
      • ‘Then the information filtered through to East End Park that Gary Holt had been called up to the international squad.’
      • ‘The ideologies we live by are often made visible and comprehensive through the stories filtering into general consciousness.’
      • ‘But he had a belief on Cup final day that his team were going to win which filtered through to the players and we got the victory.’
      • ‘At that stage, death and what it meant had only just begun to filter into my consciousness.’
      • ‘You probably could hear it, as word filtered back that he was in U.S. hands.’
      • ‘Then, finally, he held her chin, gently, so that his eyes bored directly into hers, and the words started to filter through.’
      • ‘Information has filtered out that the affected communities were provided next to no compensation and in some cases, were simply left at the mercy of floods.’
      • ‘The book was timely, arriving at a time when youth culture was just kicking off in Britain, and linked nicely with the existentialist thought slowly filtering in from France.’
      • ‘News filtered through as MPs debated the bill that will pay for the Olympic Games.’
      • ‘While there has been no word from her, the woman believes information will filter through to the foreign country she is living in.’
      • ‘Gradually the news filtered through that the latest incidents were nowhere near as bad as the bombings a fortnight ago.’
    3. 2.3British (of traffic) be allowed to pass to the left or right at a junction while traffic going straight ahead is halted.
      • ‘At 8am, traffic filtered around the closed-off Cricklade Street smoothly, but as the morning wore on, vehicles began to build up in Devizes Road and Albert Street.’
      • ‘The problem with the whole system is it is putting too much pressure on Main Street as the traffic cannot filter through New Street anymore.’
      • ‘She said new traffic lights were helping Park & Ride motorists as they filtered on to the A19 towards the roundabout, at the expense of people already on the A19.’


  • have no filter

    • Have a tendency to say exactly what one is thinking without considering the consequences:

      ‘I have no filter and I do say things that I probably shouldn't say’


Late Middle English (denoting a piece of felt): from French filtre, from medieval Latin filtrum felt used as a filter, of West Germanic origin and related to felt.