1. A letter of the alphabet.
See V. In Greek Υψιλον (Ypsilon) was pronounced /u/ (later on /y/, now /i/; see English MYTH and GIFT which both have /I/). The Romans borrowed Y directly from the Greek, because they felt that V no longer adequately represented Greek /y/. The English name of the letter - /waI/ - is of unknown origin. In Spanish, Y is called i griega; in most other European languages the Greek name is still used.