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upsilon

[yoop-suh-lon, -luh n, uhp-; especially British yoop-sahy-luh n]
noun
  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

British Dictionary definitions for upsilon particle

upsilon

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

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 particle

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 particle in Medicine

upsilon

n.
  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.

upsilon particle in Science

upsilon particle

[ŭpsə-lŏn′, yōōp-]
  1. An electrically neutral meson having a mass 18,513 times that of the electron and a mean lifetime of approximately 8.0 X 10-20 seconds. See Table at subatomic particle.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.