Upsilon

Upsilon (US: /ˈʌpsɪˌlɒn, ˈ(j)p-, -lən/, UK: /(j)pˈslən, ʊp-, -lɒn/ ; uppercase Υ, lowercase υ; Greek: ύψιλον ýpsilon [ˈipsilon]) or ypsilon /ɪp-/ is the twentieth letter of the Greek alphabet. In the system of Greek numerals, Υʹ has a value of 400. It is derived from the Phoenician waw .