Definition of tracer in English:



  • 1A person or thing that traces something or by which something may be traced, in particular.

    1. 1.1A bullet or shell whose course is made visible in flight by a trail of flames or smoke, used to assist in aiming.
      ‘the night sky turned into a light show of artillery, flares, and tracers’
      [mass noun] ‘the night was lit up by tracer’
      [as modifier] ‘tracer fire’
      • ‘On top of this, other final elements were and filmed separately and then digitally added to the shot to replicate tracer fire, smoke, and shell casings falling from the machine guns.’
      • ‘The ramp dropped, and I clawed my way through hacking tracer fire and screaming shells to a grocery store, where I bought toothpaste and some disposable razors.’
      • ‘The embedded reporter and camera see weapons fired at an unseen enemy and, if they are lucky, they may see tracers of weapons fired back.’
      • ‘Once when we were shopping, red tracer bullets were fired from the camp over the village.’
      • ‘Each of his 15 shots sailed 100 yards out across the fairway before bending, like a tracer bullet, back across the driving range.’
      • ‘At night the tracers became the only visible part of a fire fight: the space between combatants a mess of pink cobwebs.’
      • ‘As we watched, a gunner fired again and red tracer bullets made their way slowly towards us across the river.’
      • ‘The origin of the bullets and tracers - the gun flashes - were almost at eye level when Rick and I looked back inside the cockpit at the altimeter.’
      • ‘I dreamed of someday flying in a Spad, firing tracers from my machine guns at German barrage balloons or zeppelins.’
      • ‘Tonight was the real deal; everything I'd trained for was coming to fruition, complete with tracer fire and maybe a few rockets being launched down there in the dark void of Afghanistan.’
      • ‘After spotting the enemy, the gunners fired tracers to pinpoint the target, while the fourth helicopter opened fire with 2.75-inch rockets.’
      • ‘The Lt said that red tracers were friendly bullets, and the Afghan's could shoot all they wanted as long as they didn't shoot at us.’
      • ‘Then, of course, all the tracer fire started coming in, and we were really in trouble.’
      • ‘He turned the bureau's news camera on the night sky to record the tracer fire now arcing impotently towards the incoming missiles.’
      • ‘Flares and tracer bullets sliced across the night sky after the blasts.’
      • ‘It was unlike any Fourth of July show you have ever seen as the sky was full of rockets, tracers and missiles.’
      • ‘The tracer bullets burned their way in darkness across the Tidal Basin into the White House.’
      • ‘The last time I tried I kept glancing at the sky in case there were red bullet tracers, or I would suddenly jump out of bed when an American helicopter would roar across the area flying incredibly low.’
      • ‘The ball travelled like a tracer bullet and it was the shot of the day.’
      • ‘A major gunnery exercise was held to expend the last of the ship's training ammunition - the tracer fire was focused on two large red inflatable targets, nicknamed the Killer Tomatoes, launched several thousand metres away from the ship.’
    2. 1.2A substance introduced into a biological organism or other system so that its subsequent distribution may be readily followed from its colour, radioactivity, or other distinctive property.
      ‘they used radioactive carbon as a tracer’
      [mass noun] ‘transfer of tracer from spinal fluid to blood’
      • ‘Because 210 Po associates appreciably with organic matter inside cells, unlike other particlereactive nonessential metals, it could have promise as a tracer of sinking organic matter in the ocean.’
      • ‘Electrons from the tissue combine with positrons from the radioactive tracer to produce gamma rays (similar to x-rays).’
      • ‘A radioactive tracer visualized the parts of the brain that were active while different types of sounds were being processed.’
      • ‘Marine geochemists can exploit the distributions of these tracers to investigate physical, chemical, and biological processes operating in the world's oceans.’
      • ‘A spect scan can help detect cancer with the aid of cancer-seeking radioactive tracers.’
      • ‘Using vital dyes as lineage tracers, the pattern of cleavage has been shown to be invariant but complex, particularly for the ectoderm.’
      • ‘The radioactive tracer evaluated for this study, known by the brand name Zemiva, links a fatty acid to a radioisotope which is injected in the patient.’
      • ‘The use of radioactive tracers makes it possible to outline a wide range of conditions, the take-up of the tracer being detected by a radioactive scanner.’
      • ‘The researchers used two different types of radioactive tracers in the same scanning sessions with 6 patients and 6 healthy controls to simultaneously monitor two different types of brain activity.’
      • ‘The node is identified by using lymphoscintigraphy and a radioactive tracer (technetium-labeled sulfur colloid or human serum albumin).’
      • ‘Finally, our understanding of the trophic structure of the ecosystem was greatly advanced by following the tracer through the food web.’
      • ‘It relies on the difference in distribution of a radioactive tracer, such as thallium, at rest and after stress.’
      • ‘Similar to a PET scan, the SPECT scan uses radioactive tracers to help spot cancer in your body.’
      • ‘If such sites are also large enough to admit fluorescent, tracer dye molecules, the permeable areas can be visualized with an epifluorescence microscope following incubation in the tracer.’
      • ‘So they enrolled him in a study, testing a new imaging system that would allow them to follow a radioactive tracer through his brain to see the plaque that has built up around the nerve cells.’
      • ‘Tumors often use more energy than healthy tissues do and may absorb more of a radioactive tracer, which allows the tumors to appear on the scan.’
      • ‘CED distributed amounts of the tracer that were comparable to the amount of drugs needed to treat brainstem diseases.’
      • ‘A bone scan falls under the category of nuclear medicine, which means that it uses tiny amounts of radioactive materials called tracers (radionuclides).’
      • ‘The distribution of tracer was followed with PETIS.’
      • ‘The weak force is harnessed in modern hospitals in the form of radioactive tracers used in nuclear medicine.’
    3. 1.3A device which transmits a signal and so can be located when attached to a moving vehicle or other object.
      • ‘The tracer was attached and they continued their pursuit.’
      • ‘And you'll be happy to know we knew exactly where you were, we installed tracers into all the vehicles.’