infinitesimal

American  

[in-fin-i-tes-uh-muhl] / ˌɪn fɪn ɪˈtɛs ə məl /

adjective

1. exceedingly small; minute.

   Capillaries, the infinitesimal vessels in our circulatory system, are small enough that red blood cells must flow through them single-file.

2. Mathematics.

   1. immeasurably small; less than an assignable quantity.

      An infinitesimal number is never zero, but it comes pretty close.

   2. of, relating to, or involving variables having zero as a limit.

      infinitesimal calculus.

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noun

1. an infinitesimal quantity.

2. Mathematics. a variable having zero as a limit.

infinitesimal British  

/ ˌɪnfɪnɪˈtɛsɪməl /

adjective

1. infinitely or immeasurably small

2. maths of, relating to, or involving a small change in the value of a variable that approaches zero as a limit

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noun

1. maths an infinitesimal quantity

infinitesimal Scientific  

/ ĭn′fĭn-ĭ-tĕs′ə-məl /

1. Capable of having values approaching zero as a limit.

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1. A function or variable continuously approaching zero as a limit.

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

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.

Example Sentences

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

There was an infinitesimal pause, just one tiny breath.

From "When Dimple Met Rishi" by Sandhya Menon

Related Words

• imperceptible
• insignificant
• microscopic
• minuscule
• negligible