Now it happened, when Adoni-zedek king of Jerusalem heard how Joshua had taken Ai, and had utterly destroyed it; as he had done to Jericho and her king, so he had done to Ai and her king; and how the inhabitants of Gibeon had made peace with Israel, and were among them;
The word "Zedek" means "righteousness." Adonizedek has the meaning of "lord of righteousness, nearly synonymous with Melchizedek, which means `king of righteousness.'"[1]  There cannot be any doubt that Melchizedek was a "Priest of God Most High," as emphatically declared in  Genesis 14:18, making it absolutely certain that Melchizedek was a monotheist and a worshipper of the One True and Almighty God.  Otherwise, Abraham's paying tithes to him, and his being singled out in the N.T. as a Great Type of the Son of God Himself  (Hebrews 7:1ff) would make no sense at all.  The expression "God Most High" receives further light in the N.T., where the expression is found five times: (1) in  Mark 5:7, where a demon protested an order from Christ, addressing Jesus Christ as, "Jesus, thou Son of God Most High"; (2)  Luke 8:28 states that a demon, pleading with Christ not to torment him, addressed Our Lord as, "Thou Son of the Most High God"; (3) the Christian martyr Stephen declared that, "The Most High dwelleth not in temples made with hands"; (4) the demon-possessed girl who followed Paul and Silas for days at Philippi, continually cried out, "These men are servants of the Most High God, who proclaim unto you the way of salvation"; and (5) the passage in  Hebrews 7:1 affirms that, "Melchizedek was a priest of the Most High God."