Tetrarch (?), n. [L. tetrarches, Gr. &unr_;, &unr_;; tetra- (see Tetra-) + &unr_; a ruler, &unr_; to lead; rule: cf. F. tétrarque. See Arch, a.] (Rom. Antiq.) A Roman governor of the fourth part of a province; hence, any subordinate or dependent prince; also, a petty king or sovereign.
[1913 Webster]