governor of a fourth part

properly the sovereign or governor of the fourth part of a country. (Matthew 14:1; Luke 3:1; 9:7; Acts 13:1) The title was, however, often applied to any one who governed a Roman province, of whatever size. The title of king was sometimes assigned to a tetrarch. (Matthew 14:9; Mark 6:14,22)

-A Roman ruler Mt 14:1

Strictly the ruler over the fourth part of a province; but the word denotes a ruler of a province generally (Matt. 14:1; Luke 3:1, 19; 9:7; Acts 13:1). Herod and Phasael, the sons of Antipater, were the first tetrarchs in Palestine. Herod the tetrarch had the title of king (Matt. 14:9).