Achor

Achor - trouble, a valley near Jericho, so called in consequence of the trouble which the sin of Achan caused Israel (Josh. 7:24,26). The expression "valley of Achor" probably became proverbial for that which caused trouble, and when Isaiah (Isa. 65:10) refers to it he uses it in this sense: "The valley of Achor a place for herds to lie down in;" that is, that which had been a source of calamity would become a source of blessing. Hosea also (Hos. 2:15) uses the expression in the same sense: "The valley of Achor for a door of hope;" that is, trouble would be turned into joy, despair into hope. This valley has been identified with the Wady Kelt.

From Easton's Bible Dictionary (1897)