“Tetrarch,” meaning ‘ruler over one fourth’ of a province, was a term applied to a minor district ruler or territorial prince. However, popularly he may have been called King, as was Archelaus.—Mt 14:9; Mr 6:14, 22, 25-27.
Herod, though it was not pleasing to him, cravenly gave in to save face before those attending the celebration and because of his oath. (However, under the Law he would not be bound by an oath to perform an illegal act, such as murder.)—Mt 14:3-12; Mr 6:17-29.