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
upsilon in American English
(ˈupsəˌlɑn; ˈʌpsəˌlɑn)
noun
1.
the twentieth letter of the Greek alphabet (Y, υ)
2. US
any of a group of short-lived elementary particles having a mass about ten times greater than that of a proton
Word origin
LGr y psilon, lit., simple u (to distinguish from oi, of the same sound in LGr)