Tetrarch

(Synop., § 130), n. [Gr. τετράρχης, τέ-τραρχος, from τέτρα, four, and ἀρχός, a ruler, ἄρχειν, to lead, rule; Lat. tetrarches, Fr. tétrarque, Pr. tetrarcha.] (Rom. Antiq.) A Roman governor of the fourth part of a province; a subordinate prince; hence, any petty king or sovereign.

a. Four. [Obs. and rare.] “Tetrarch elements.” Fuller.