Tetrarch - Vine's Expository Dictionary of New Testament Words
Tetrarch[ A-1,Noun,5076,tetraarches / tetrarches ] denotes one of four rulers" (tetra, "four," arche, "rule"), properly, "the governor of the fourth part of a region;" hence, "a dependent princeling," or "any petty ruler" subordinate to kings or ethnarchs; in the NT, Herod Antipas, Matthew 14:1; Luke 3:19; Luke 9:7; Acts 13:1.
[ B-1,Verb,5075,tetraacheo / tetrarcheo ] "to be a tetrarch," occurs in Luke 3:1 (thrice), of Herod Antipas, his brother Philip and Lysanias. Antipas and Philip each inherited a fourth part of his father's dominions. Inscriptions bear witness to the accuracy of Luke's details.