Jahaz, Jahaza, Jahazah, and Juhzah
(trodden down), under these four forms is given in the Authorized Version the name of a place which in the Hebrew appears as Yahats and Yahtsah. At Jahaz the decisive battle was fought between the children of Israel and Sihon king of the Amorites (Numbers 21:23; Deuteronomy 2:32; Judges 11:20). It was in the allotment of Reuben (Joshua 13:18). Like many others relating to the places east of the Dead Sea, the question of its site must await further research.
Smith's Bible Names Dictionary (1866)