in·​fin·​i·​tes·​i·​mal | \ (ˌ)in-ˌfi-nə-ˈte-sə-məl, -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 , -​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


an infinitesimal moment in time a soft drink with only an infinitesimal amount of caffeine

Recent Examples on the Web: Adjective

The reality, however, is that planning the coming summit meeting between President Trump and Kim Jong-un to discuss North Korea’s nuclear future will require deciding countless, infinitesimal details, often via tricky diplomatic negotiations. New York Times, "Planning Trump-Kim Meeting: Who Sits Where, What Will They Eat and Who Pays?," 3 June 2018 Still, by the five-year mark, the fish had almost died off in the lake — near-extinction of a species due to an infinitesimal amount of a hormone. Rachael Moeller Gorman, Good Housekeeping, "Is Your Tap Water Safe?," 15 Aug. 2012 And the marginal cost of overpaying is infinitesimal relative to that base. Peter Kafka, Recode, "Here’s what HBO’s new boss really said about the company’s plans under AT&T," 10 July 2018 Assuming Boogie keeps his ego in check—and the Warriors’ culture seems to do a good job of that—the margin of error for this team went from small to infinitesimal. Rohan Nadkarni,, "The Case For LeBron to Back Out of His Deal With the Lakers," 3 July 2018 For the masses of aspiring players, whose chances of succeeding are infinitesimal, the costs are human and in many cases quite brutal. Laurent Dubois, The Atlantic, "How Not to Scout for Soccer Talent," 14 June 2018 After all, as others have pointed out, dockless bike graveyards are infinitesimal compared to their motor-vehicle counterparts. Eben Weiss, Outside Online, "Bike Share Can Save Our Cities—If We Let It," 13 June 2018 In fact, the film industry, despite its very high cultural profile, is an almost infinitesimal factor in the states $2.6 trillion economy, and not even very important in Southern California. San Francisco Chronicle, "One welfare boost for the poor, another for the rich," 11 June 2018 According to the Red Cross Society of China, the world’s most populous nation is home to roughly 8 million people of short stature—meaning that the Kingdom only houses an infinitesimal proportion. Charlie Campbell / Kunming, Time, "Finding Love in the Kingdom of the Little People," 1 June 2018

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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Last Updated

13 Jan 2019

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The first known use of infinitesimal was in 1706

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English Language Learners Definition of infinitesimal

: extremely small


in·​fin·​i·​tes·​i·​mal | \ in-ˌfi-nə-ˈte-sə-məl \

Kids Definition of infinitesimal

: extremely small The chance of winning is infinitesimal.

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