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[in-fin-i-tes-uh-muh l] /ˌɪn fɪn ɪˈtɛs ə məl/
indefinitely or exceedingly small; minute:
infinitesimal vessels in the circulatory system.
immeasurably small; less than an assignable quantity:
to an infinitesimal degree.
of, relating to, or involving infinitesimals.
an infinitesimal quantity.
Mathematics. a variable having zero as a limit.
1645-55; < New Latin infīnītēsim(us), equivalent to Latin infīnīt(us) infinite + -ēsimus suffix of ordinal numerals + -al1
Related forms
infinitesimality, infinitesimalness, noun
infinitesimally, adverb Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for infinitesimal
  • Neither infinitesimal time nor infinitesimal space is possible.
  • But this temporal frame captures only a tiny portion-in fact, an infinitesimal one-of the entire future.
  • We do not and never will due to the infinity and infinitesimal nature of the universe.
  • It encourages people to invest their dreams, their hopes for a better future, into an infinitesimal probability.
  • When they collide, they explode into dozens of other particles, even more infinitesimal and fleeting.
  • The mouth washings had removed all but one microgram, an infinitesimal but nevertheless hazardous amount.
  • But you cannot weigh something to the infinitesimal number of decimal places, parts in a billion.
  • It is infinitesimal which is a positive nonstandard number which is smaller than any positive real number.
  • The displacement was infinitesimal on the scale of the sky, and a measure of impressive navigational precision.
  • They would develop together, in infinitesimal stages, over millions of years.
British Dictionary definitions for infinitesimal


infinitely or immeasurably small
(maths) of, relating to, or involving a small change in the value of a variable that approaches zero as a limit
(maths) an infinitesimal quantity
Derived Forms
infinitesimally, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for infinitesimal

1710 (1650s as a noun), "infinitely small," from Modern Latin infinitesimus, from Latin infinitus "infinite" (see infinite) + -esimus, as in centesimus "hundredth." Related: Infinitesimally.

Online Etymology Dictionary, © 2010 Douglas Harper
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infinitesimal in Science
Adjective  Capable of having values approaching zero as a limit.

Noun  A function or variable continuously approaching zero as a limit.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Article for infinitesimal

in mathematics, a quantity less than any finite quantity yet not zero. Even though no such quantity can exist in the real number system, many early attempts to justify calculus were based on sometimes dubious reasoning about infinitesimals: derivatives were defined as ultimate ratios of infinitesimals, and integrals were calculated by summing rectangles of infinitesimal width. As a result, differential and integral calculus was originally referred to as the infinitesimal calculus. This terminology gradually disappeared as rigorous concepts of limit, continuity, and the real numbers were formulated.

Learn more about infinitesimal with a free trial on
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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