Clearchus play biographical name Cle·ar·chus \klē-ˈär-kəs\ Definition of Clearchus 5th cent. b.c. Greek soldier; gov. of Byzantium Learn More about clearchus Britannica.com: Encyclopedia article about Clearchus Seen and Heard What made you want to look up Clearchus? Please tell us where you read or heard it (including the quote, if possible).