ad'-ver-sa-ri, ad'-ver-sa-ri: This word (in the singular or plural) is used in the Old Testament to render different Hebrew words. In thirty-two cases the word corresponds to the noun tsar, or the verb tsarar. This noun is the ordinary word for "foe" or "adversary." In twelve passages the Hebrew word, of which "adversary" is the translation, is saTan = noun or saTan = verb. This stem means "to oppose," or "thwart" anyone in his purpose or claims.
⇒See the definition of adversary in the KJV Dictionary
The angel of Yahweh was saTan to Balaam (Nu 22:22). The word often denotes a political adversary (1Ki 11:14,23,25). In four cases (namely, Prologue to Job; Zec 3:1-2; 1Ch 21:1; Ps 109:6) the King James Version retains Satan as the rendering. But it is only in 1 Chronicles that the word is used without the article, that is, strictly as a proper name. The Septuagint gives diabolos, as the rendering, and both in Job and Zechariah, Satan is portrayed as the "false accuser." In two cases "adversary" represents two Hebrew expressions which mean the "opponent in a suit" or "controversy" (Job 31:35; Isa 50:8).
In the New Testament "adversary" represents: (1) antikeimenoi, the participle of a verb which means "to be set over against," "to be opposed" (Lu 13:17; Php 2:8). (2) antidikos, "opponent in a lawsuit," "prosecutor" (Mt 5:25; Lu 12:58; 18:3; 1Pe 5:8). According to the last passage the devil is the "accuser" or "prosecutor" of believers, but according to another writer they have an "advocate" or "counselor for the defense" with the Father (1Jo 2:1). In one passage (Heb 10:27) "adversary" represents a Greek word, hupenantios, which means "set over against," "contrary to"--a word used in classical Greek and in the Septuagint.
⇒See also the McClintock and Strong Biblical Cyclopedia.