The Greek alphabet on a black figure vessel, with a V-shaped upsilon. Etymology. The name of the letter was originally just "υ" (y; also called hy, hence "hyoid", meaning "shaped like the letter υ"), but the name changed to "υ ψιλόν" u psilon 'plain υ' to distinguish it from οι, which had come to have the same [y] pronunciation. [7] Pronunciation.