The meaning of Tetrarch in the Bible
(From International Standard Bible Encyclopedia)

te'-trark, tet'-rark tetrarches): As the name indicates it signifies a prince, who governs one-fourth of a domain or kingdom. The Greeks first used the word. Thus Philip of Macedon divided Thessaly into four "tetrarchies." Later on the Romans adopted the term and applied it to any ruler of a small principality. It is not synonymous with "ethnarch" at least the Romans made a distinction between Herod "tetrarch" of Galilee, Philip "tetrarch" of Trachonitis, Lysanias "tetrarch" of Abilene, and Archelaius "ethnarch" of Judea (BJ, II, vi, 3; Ant, XVII, xi, 4). The title was often conferred on Herodian princes by the Romans, and sometimes it was used courteously as a synonym for king (Matthew 14:9; Mark 6:14). In the same way a "tetrarchy" was sometimes called a kingdom.

Henry E. Dosker

See more on the meaning of Tetrarch in the Bible:
Tetrarch {Easton's Bible Dictionary}
Tetrarch {Hitchcock's Bible Name}

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