infinitesimal
Americanadjective
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exceedingly small; minute.
Capillaries, the infinitesimal vessels in our circulatory system, are small enough that red blood cells must flow through them single-file.
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Mathematics.
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immeasurably small; less than an assignable quantity.
An infinitesimal number is never zero, but it comes pretty close.
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of, relating to, or involving variables having zero as a limit.
infinitesimal calculus.
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noun
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an infinitesimal quantity.
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Mathematics. a variable having zero as a limit.
adjective
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infinitely or immeasurably small
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maths of, relating to, or involving a small change in the value of a variable that approaches zero as a limit
noun
Other Word Forms
- infinitesimality noun
- infinitesimally adverb
- infinitesimalness noun
Etymology
Origin of infinitesimal
First recorded in 1645–55; from New Latin infīnītēsim(us), equivalent to Latin infīnīt(us) infinite + -ēsimus suffix of ordinal numerals + -al 1
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
But a car either complies or it does not, no matter how infinitesimal the infraction.
From BBC • Nov. 23, 2025
Suddenly, the infinitesimal chances of the U.S.—down to 0.1% at one point during the day, according to Data Golf—began to creep upward with wins from its first two players.
From The Wall Street Journal • Sep. 28, 2025
Art often is just a business, but a dangerous one: Changing people by an infinitesimal degree, Castleberry knows, has a way of thoroughly warping and wrecking human lives.
From Los Angeles Times • Mar. 6, 2025
El universo tal como lo conocemos ahora tiene 14 mil millones de años, lo que parece mucho tiempo, pero es solo una porción infinitesimal de los billones y trillones de años de oscuridad por venir.
From New York Times • May 6, 2023
The infinitesimal time period o drops right out of the equation, oy/ox becomes y/x, and o need never be thought of again.
From "Zero: The Biography of a Dangerous Idea" by Charles Seife
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
