Definition of infinitesimal in US English:



  • Extremely small.

    ‘an infinitesimal pause’
    • ‘Minute, infinitesimal amounts of chemical contaminants crossing the placenta can cause cancer in young adults decades later.’
    • ‘Or maybe, we fear that if we pause for even an infinitesimal second, someone else will grab our place and get ahead?’
    • ‘He blinked and rapidly adjusted the viewer's dials, but what seemed to be a tiny, almost infinitesimal flashing green light on one end of the diamond, did not disappear.’
    • ‘Any way you look at it, the number is infinitesimal.’
    • ‘It was a pause so infinitesimal that I almost didn't catch it, but I knew what I glimpsed.’
    • ‘There was an infinitesimal pause before the last word, as the principal tactfully searched for the right word, but an untrained ear wouldn't have noticed it.’
    • ‘But the new puritans argue that any risk, no matter how infinitesimal, is intolerable.’
    • ‘There are infinitesimal numbers of cycles of improvement and degradation, one following the other like the phases of waxing and waning moons.’
    • ‘The changes in timing a hit are almost laughably infinitesimal but are utterly crucial to the way the foil is used.’
    • ‘The rock is already slipping down by infinitesimal degrees.’
    • ‘But now, increasingly, those infinitesimal aspects of everyday life, taken together, are seen to have a broader importance and even might be the keys to a certain kind of political action or subversion.’
    • ‘Really, what I want to do is impossible, for any listing of an endless series is doomed to be infinitesimal.’
    • ‘I don't have an explanation - I'd like to have one but I don't - but in the meantime, without evidence, the odds of your position being right are so infinitesimal as to be irrelevant.’
    • ‘So, living in London and desperately weak of will, you get poisoned by choice; overwhelming and almost infinitesimal choice.’
    • ‘There isn't a single person in all these millions, including the president of the pencil company, who contributes more than a tiny, infinitesimal bit of know-how.’
    • ‘And that's critical to the analysis of the solar wind, the particles of which contain infinitesimal traces of the 83 naturally occurring elements.’
    • ‘People worry more about infinitesimal risks they feel are imposed on them than they do about the more important ones they voluntarily bring upon themselves.’
    • ‘For whatever infinitesimal consolation it may offer, Wellstone could feel the victory coming.’
    • ‘It is fair to say that in the entire North Western area that the level of infrastructural investment has been infinitesimal in comparison to spending on the east coast.’
    • ‘I seek leave to table from the New England Journal of Medicine a recent definitive study showing that intellectual impairment of children can occur even with extremely infinitesimal amounts of lead.’
    minute, tiny, minuscule, extremely small, very small
    View synonyms


  • An indefinitely small quantity; a value approaching zero.

    • ‘The book shows how this notion can be used to form various kinds of infinities such as the projective plane, transfinite numbers, and infinitesimals.’
    • ‘Since his work made its appearance just before the dawn of calculus, infinitesimals will be used in the sequel.’
    • ‘Also in 1786 he again worked on his ideas for the differential and integral calculus, giving a new treatment of infinitesimals.’
    • ‘These two concepts, infinitesimals and infinite quantities, however, were stirring great philosophical dilemmas.’
    • ‘He began to study the geometry of infinitesimals and wrote to Oldenburg at the Royal Society in 1674.’


Although this long word is commonly assumed to refer to large numbers, infinitesimal describes only very small size. While there may be an infinite number of grains of sand on the beach, a single grain may be said to be infinitesimal


Mid 17th century: from modern Latin infinitesimus, from Latin infinitus (see infinite), on the pattern of centesimal.