upsilon

n. twentieth letter of the Greek alphabet

Upsilon (uppercase Υ, lowercase υ) is the 20th letter of the Greek alphabet. In the system of Greek numerals it has a value of 400. It is derived from the Phoenician waw. In early Greek it was pronounced like "euw" u or English oo, IPA  . In Classical Greek, it was pronounced like French u or German ü, IPA —a sound that is not found in most dialects of English. In Modern Greek it is pronounced like continental i or English ee, IPA , and in diphthongs, or . In ancient Greek it occurred in both long and short versions, but this distinction has been lost in Modern Greek.
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Noun
1. the 20th letter of the Greek alphabet
(hypernym) letter, letter of the alphabet, alphabetic character
(member-holonym) Greek alphabet

n. upsilon, twentieth letter of the Greek alphabet

n. upsilon, twentieth letter of the Greek alphabet