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The 20th letter of the Greek alphabet. See Table at alphabet.
[Late Greek ū psīlon, simple u (from the fact that oi was given the same pronunciation in Late Greek as u) : ū, hū, the letter U + psīlon, neuter of psīlos, simple (written with one letter as opposed to two).]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Letters of the Alphabet (Foreign)) the 20th letter in the Greek alphabet (Υ, υ), a vowel, transliterated as y or u
[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 and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
up•si•lon(ˈyup səˌlɒn, -lən, ˈʌp-; esp. Brit. yupˈsaɪ lən)
1. the 20th letter of the Greek alphabet (Y, υ).
2. Also called up′silon par`ticle. any of a family of heavy, short-lived, neutral mesons that are composed of a bottom quark and its antiquark. Symbol:Y, υ
[1615–25; < Late Greek ŷ psīlón literally, simple u (to distinguish it from the diagraph oi, pronounced the same in Late Greek]
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|Noun||1.||upsilon - the 20th letter of the Greek alphabet|
Greek alphabet - the alphabet used by ancient Greeks
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