infinitesimal

1 of 2

adjective

in·​fin·​i·​tes·​i·​mal (ˌ)in-ˌfi-nə-ˈte-sə-məl How to pronounce infinitesimal (audio)
-zə-məl
Synonyms of infinitesimal
1
: immeasurably or incalculably small
an infinitesimal difference
2
: taking on values arbitrarily close to but greater than zero

infinitesimal

2 of 2

noun

: an infinitesimal quantity or variable

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What is the origin of infinitesimal?

Infinite, as you probably know, means "endless" or "extending indefinitely." It is ultimately from Latin infīnītus, the opposite of fīnītus, meaning "finite." The notion of smallness in infinitesimal derives from the mathematical concept that a quantity can be divided endlessly; no matter how small, it can be subdivided into yet smaller fractions, or infinitesimals. The concept was still in its infancy in the early 1700s when Irish philosopher George Berkeley observed that some people "assert there are infinitesimals of infinitesimals of infinitesimals, etc., without ever coming to an end." He used the word in a mathematical sense, too, referring to "infinitesimal parts of finite lines." Later, the adjectival form acquired a general sense applicable to anything too small to be measured.

Examples of infinitesimal in a Sentence

Adjective an infinitesimal moment in time a soft drink with only an infinitesimal amount of caffeine
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Adjective
The chances of that are infinitesimal, he’s told. Natalie Oganesyan, Deadline, 23 Mar. 2026 Over the course of decades, people inevitably evolve in both infinitesimal and significant ways. Patricia Neligan, AJC.com, 7 May 2026
Noun
But neither a chart of geology’s eons, eras, and periods, nor a calculus of infinitesimals, can eliminate a sense of awe in the face of geological time. Lewis Hyde, Harpers Magazine, 18 June 2025 Since then, Parker has persistently sought meaning in the infinitesimal and evanescent. Jonathon Keats, Forbes, 20 May 2022 See All Example Sentences for infinitesimal

Word History

Etymology

Adjective

borrowed from New Latin infīnītēsimālis, from infīnītēsimus "infinite in rank" (from Latin infīnītus "having no limit, infinite entry 1" + -ēsimus, suffix of higher ordinal numbers) + Latin -ālis -al entry 1 — more at vigesimal

Noun

New Latin infīnītēsimus "infinite in rank" + -al entry 2 — more at infinitesimal entry 1

First Known Use

Adjective

1710, in the meaning defined at sense 2

Noun

1706, in the meaning defined above

Time Traveler
The first known use of infinitesimal was in 1706

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Cite this Entry

“Infinitesimal.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/infinitesimal. Accessed 8 Jul. 2026.

Kids Definition

infinitesimal

adjective
in·​fin·​i·​tes·​i·​mal
(ˌ)in-ˌfin-ə-ˈtes-ə-məl
: too small to be measurable
infinitesimally
-mə-lē
adverb

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