Theseus Syllabification: (The·se·us)Pronunciation: /ˈTHēsēəs, -syo͞os/ Greek MythologyDefinition of Theseus the legendary hero of Athens, son of Poseidon (or, in another account, of Aegeus, king of Athens) and husband of Phaedra. He slew the Cretan Minotaur with the help of Ariadne. Theseus in other Oxford dictionaries Definition of Theseus in the British & World English dictionary