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 (ŭp′sə-lŏn′, yo͞op′-)
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).]


(ˈʌpsɪˌlɒn; juːpˈsaɪlən)
(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]


(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]
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.upsilon - the 20th letter of the Greek alphabetupsilon - the 20th letter of the Greek alphabet
Greek alphabet - the alphabet used by ancient Greeks
alphabetic character, letter of the alphabet, letter - the conventional characters of the alphabet used to represent speech; "his grandmother taught him his letters"