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[yoop-suh-lon, -luh n, uhp-; especially British yoop-sahy-luh n] /ˈyup səˌlɒn, -lən, ˈʌp-; especially British yupˈsaɪ lən/
the 20th letter of the Greek alphabet (Υ, υ).
the vowel sound represented by this letter.
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.
Origin of upsilon
1615-25; < Late Greek ŷ psīlón literally, simple u (to distinguish it from the digraph oi, pronounced the same in LGk) Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for upsilon


/ˈʌpsɪˌlɒn; juːpˈsaɪlən/
the 20th letter in the Greek alphabet (Υ, υ), a vowel, transliterated as y or u
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
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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.

Online Etymology Dictionary, © 2010 Douglas Harper
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upsilon in Medicine

upsilon up·si·lon or yp·si·lon (ŭp'sə-lŏn', yōōp'-)

Symbol υ The 20th letter of the Greek alphabet.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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