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
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
Explanation
When it's incalculably small, when teensy seems large compared to it, then it is infinitesimal. "The equipment was so sensitive that even the infinitesimal dust molecules that swept in with the open door altered the readings." Infinitesimal is such an extreme description of a microscopic something that the word is used as an exaggeration more often than to describe something actually quite small. "The chances of Roxy going out on a date with Norbert were infinitesimal. She barely even knew he existed." Infinitesimal is derived from the root infinite, which usually conjures up thoughts of immeasurably large quantities or sizes. But in this case, infinite connotes something immeasurably small.
Vocabulary lists containing infinitesimal
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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 after a career spent measuring progress in sometimes infinitesimal steps, he has shared experiences that are already proving valuable.
From Los Angeles Times • May 18, 2026
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
While I appreciate the sentiment, there’s an infinitesimal flaw in Kurkjian’s premise.
From Seattle Times • May 15, 2024
A proton is an infinitesimal part of an atom, which is itself of course an insubstantial thing.
From "A Short History of Nearly Everything" by Bill Bryson
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.
