adversary
n.an opponent or enemy in a fight, game, or argument. You use this word for someone you are actively competing against.
n.an opponent in a contest, conflict, or dispute. Often implies a long-standing or formidable opposition rather than a temporary rival.
“The boxer respected his adversary after the long match.”
“In the final round of the debate, she faced her most difficult adversary yet.”
“The two political leaders had been adversaries for decades, yet they maintained a level of mutual respect that allowed for occasional diplomatic breakthroughs.”
Frequently paired with adjectives like 'formidable', 'worthy', or 'old'.
“But what I’m concerned about is that we’re sending a message of weakness to our primary adversaries.”
From Middle English adversarie, from Anglo-Norman aversaire (in Wace's Life of Saint Margaret) and Old French aversier, aversaire (French adversaire), from Latin adversārius, from adversus (“turned toward”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.