Thayer's Greek Lexicon

 Aretes = "graver"
1. An Arabian king

He made war in 36 A.D. on his son-in-law Herod Antipas for having
divorced his daughter; and with such success as completely to
destroy his army. In consequence of this, Vitellius, governor of
Syria, being order by Tiberius to march an army against Aretes,
prepared for war. But Tiberius meantime having died, (Mar. 16, 37.,
he recalled his troops from march, dismissed them to winter
quarters, and departed for Rome. After his departure Aretas held
sway over the region of Damascus (how acquired we do not know), and
placed an ethnarch over the city, who tried to capture Paul.