Hastings' Dictionary of the Bible (1898)
TE'TRARCH. This title was given to a sovereign prince, and strictly denotes one who governs the fourth part of a province or kingdom. Matt 14:1. In our Scriptures, however, it is applied to any one who governed a province of the Roman empire, whatever portion of the territory might be within his jurisdiction. The tetrarch had the title of king;. Matt 14:9.