Hesychius of Alexandria (hēsĭk`ēəs), fl. 5th cent.?, Alexandrian grammarian. Hesychius is known as the compiler of an invaluable lexicon, a glossary of unusual words and expressions occurring in Greek writings. The material is drawn from special languages (e.g., medical), from older poets, and from various dialects and languages. It is the source of virtually all the material now available on certain vanished languages, such as ancient Macedonian.