The difference between Foe and Opponent

When used as nouns, foe means an enemy, whereas opponent means one who opposes another.

When used as adjectives, foe means hostile, whereas opponent means opposing.

check bellow for the other definitions of Foe and Opponent

Opponent as a noun (historical):

One who opposes another; one who works or takes a position against someone or something; one who attempts to stop the progress of someone or something. One who opposes another physically (in a fight, sport, game, or competition). One who opposes another in words (in a dispute, argument or controversy). One who is opposed or objects (to a policy, course of action or set of ideas). The participant who opens an academic debate by putting forward objections to a theological or philosophical thesis.

Examples:

"The person who ran against her in the last election proved to be a formidable opponent."

"During the crackdown, many opponents of the regime were arrested."

"She was a dedicated opponent of the death penalty."

Opponent as an adjective (obsolete):

Opposing; adverse; antagonistic.
Opponent as an adjective (obsolete):

Situated in front; opposite.