ad·ver·sary 1 /'ad-vər-ˌser-ē/ n: one that contends with or opposes another; esp: any of the opposing parties in a legal action
adversary 2 adj: of, relating to, or involving opposing parties or interests; specif: of, relating to, or involving a system of justice in which opposing parties usu. represented by counsel present evidence to an impartial decision-maker (as a jury) by a process of questioning witnesses under the supervision of a judge compare accusatorial, inquisitorial
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.