|upsilon (ˈʌpsɪˌlɒn, juːpˈsaɪlən)|
|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]|
upsilon up·si·lon or yp·si·lon (ŭp'sə-lŏn', yōōp'-)
Symbol υ The 20th letter of the Greek alphabet.