Definition of: tetrarch

(tet′rärk, tē′trärk) noun
1. The governor of one of four divisions of a country or province.
2. A tributary prince under the Romans; a subordinate ruler.
3. Anciently, in the Greek army, the commander of a subdivision of a phalanx. [<LL tetrarcha <L tetrarches <Gk. tetrarchēs <tetra- four + archos ruler]
—tet·rar·chy (tet′rär·kē, tē′trär-), tet·rarch·ate (tet′rär·kāt, -kit, tē′trär-) noun