Satan (H7853) as a verb means to oppose, to be an adversary, to accuse. As a noun it denotes the adversary or accuser. In early usage it can describe a human or angelic opponent; in later texts it becomes the proper name of the chief spiritual adversary.
The heavenly accuser appears in Job 1–2 as one who challenges the integrity of the righteous before God. In Zechariah 3, Satan stands to accuse the high priest Joshua — yet the LORD rebukes him. The New Testament (Greek diabolos/Satanas) carries these themes into full spiritual warfare: the accuser of the brethren is cast down (Revelation 12:10). Christ's victory on the cross silences the ultimate accusation.