Is adversaire masculine or feminine?
l'adversaire
Both le and la are accepted for this word.
In context
J'ai sous-estimé la force de mon adversaire.
I have underestimated the strength of my opponent.
Il n'a aucune chance contre son adversaire.
He doesn't stand a chance against his opponent.
Les deux partis politiques sont des adversaires irréconciliables.
The two political parties are irreconcilable foes.