in·​fin·​i·​tes·​i·​mal | \ (ˌ)in-ˌfi-nə-ˈte-sə-məl How to pronounce infinitesimal (audio) , -zə-məl \

Definition of infinitesimal

 (Entry 1 of 2)

1 : immeasurably or incalculably small an infinitesimal difference
2 : taking on values arbitrarily close to but greater than zero



Definition of infinitesimal (Entry 2 of 2)

: an infinitesimal quantity or variable

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Other Words from infinitesimal


infinitesimally \ (ˌ)in-​ˌfi-​nə-​ˈte-​sə-​mə-​lē How to pronounce infinitesimally (audio) , -​zə-​mə-​ \ adverb

What is the origin of infinitesimal?


Infinite, as you probably know, means "endless" or "extending indefinitely." It is ultimately from Latin infinitus, the opposite of finitus, 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 1710 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 adjective in a mathematical sense, too, referring to "infinitesimal parts of finite lines." Less than a quarter century later, the adjective had 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: Adjective The board will handle an infinitesimal slice of those, maybe 25 or 30 in its first year—and Facebook is obliged to respect its decisions only in those individual cases. Steven Levy, Wired, "Why Mark Zuckerberg’s Oversight Board May Kill His Political Ad Policy," 28 Jan. 2020 Think of the World Wide Web, the power grid and the universe, of which the Milky Way is an infinitesimal node in a seemingly boundless network of galaxies. Max Bertolero, Scientific American, "How the Mind Emerges from the Brain's Complex Networks," 11 July 2019 The margin separating one winner from the next is often infinitesimal. Cnt Editors, Condé Nast Traveler, "How Do the Readers' Choice Awards Work?," 7 Oct. 2019 But Geoffrey Eaton, an attorney for the airmen, argued that the odds of transmitting HIV in combat are infinitesimal and should not limit their deployment or lead to their discharge. Denise Lavoie, San Diego Union-Tribune, "Appeals court asked to halt discharge of Airmen with HIV," 18 Sep. 2019 Even this little spot on this little planet in a galaxy that is but an infinitesimal speck in a universe, humans are wise to know their place. Los Angeles Times, "Review: At Mt. Wilson, cosmic sound art reaches far beyond a mere moon landing," 21 July 2019 Unfortunately, the alternatives for traditional conservatives are not great, and the odds of another Republican winning the GOP nomination in 2020 are infinitesimal. Jim Geraghty, National Review, "A Buffet Table of Bad Options for Anti-Trump Conservatives in 2020," 21 Aug. 2019 Wilds understands his odds of making the 53-man roster are infinitesimal. Eric Branch,, "Brandon Wilds’ story: 49ers’ running back came through after coming off couch," 14 Aug. 2019 Granted, my contribution was small — infinitesimal would be overstating it. Ellen Albanese,, "Get stuck on sticks with a visit to ‘A Passing Fancy’," 16 July 2019 Recent Examples on the Web: Noun Infinities implicitly pervade many familiar mathematical concepts, such as the idea of points as mentioned above, the idea of the continuum, and the concept of infinitesimals in calculus. Quanta Magazine, "Is Infinity Real?," 16 June 2016

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'infinitesimal.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of infinitesimal


1710, in the meaning defined at sense 2


1706, in the meaning defined above

History and Etymology for infinitesimal


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


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

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Time Traveler for infinitesimal

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The first known use of infinitesimal was in 1706

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Last Updated

10 Feb 2020

Cite this Entry

“Infinitesimal.” Dictionary, Merriam-Webster, Accessed 29 Feb. 2020.

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More Definitions for infinitesimal


How to pronounce infinitesimal (audio)

English Language Learners Definition of infinitesimal

: extremely small


in·​fin·​i·​tes·​i·​mal | \ in-ˌfi-nə-ˈte-sə-məl How to pronounce infinitesimal (audio) \

Kids Definition of infinitesimal

: extremely small The chance of winning is infinitesimal.

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