• synonyms


[yoop-suh-lon, -luh n, uhp-; especially British yoop-sahy-luh n]
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  1. the 20th letter of the Greek alphabet (Υ, υ).
  2. the vowel sound represented by this letter.
  3. Also called upsilon particle. Physics. any of a family of heavy, short-lived, neutral mesons that are composed of a bottom quark and its antiquark. Symbol: Υ, υ
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Origin of upsilon

1615–25; < Late Greek ŷ psīlón literally, simple u (to distinguish it from the digraph oi, pronounced the same in LGk)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for upsilon

Historical Examples

  • This species is the ypsilon of Borkhausen, and the upsilon of other authors.

    The Moths of the British Isles, Second Series

    Richard South

  • She issued an order, therefore, that for a certain time Upsilon was to have no playthings.

British Dictionary definitions for upsilon


  1. the 20th letter in the Greek alphabet (Υ, υ), a vowel, transliterated as y or u
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Word Origin

C17: from Medieval Greek u psilon simple u, name adopted for graphic u to avoid confusion with graphic oi, since pronunciation was the same for both in Late Greek
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for upsilon

"20th letter of the Greek alphabet," 1640s, from Greek u psilon, literally "a mere (or bare) 'u;' " so called in contradistinction to the diphthongs -oi-, -ei-, which are pronounced exactly like upsilon.

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Online Etymology Dictionary, © 2010 Douglas Harper

upsilon in Medicine


  1. The 20th letter of the Greek alphabet.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.