One that opposes another in a battle, contest, controversy, or debate
See syn. study at
He knew his adversary's overall military capability.
He was a determined adversary of the Reformation.
He was looking for, in his words, "a worthy adversary."
For eighteen years he showed himself no unworthy adversary of Sulla, Lucullus and Pompey.
In 1877 he fought a duel in which he killed his adversary, a rival journalist.