I was tired, at any rate; but had I been as fresh as when I rose, I could see it was in vain for me to contend in speed with such an adversary.
There are no more uses of "adversary" in the book.
Show samples from other sources
Then, again, our military training is in many respects superior to that of our adversaries.
Thucydides -- Pericles’s Funeral Oration
Finally, it was rumored, there would be complete information-sharing among all of these previously disconnected and even adversarial entities, and when they were coordinated, and once all the health data they’d collected was shared, most of this made possible through the Circle and more important, TruYou, viruses could be stopped at their sources, diseases would be tracked to their roots.