Numbers 25:3 - Joseph Benson’s Commentary on the Old and New Testaments

Joined himself The word implies a forsaking God, to whom they were joined, and a turning to, and strict conjunction with, this false god. Baal-peor Called Baal, by the name common to many false gods, and especially to those that represented any of the heavenly bodies; and Peor, either from the hill Peor, where he was worshipped, Numbers 23:28; or rather from a verb signifying to open and uncover, because of the obscene posture in which the idol was set, as Priapus was; or because of the filthiness which was exercised in his worship.