opponent
n. countable B2 Upper Intermediate Oxford US //əˈpoʊnənt// UK //əpˈəʊnənt// op·po·nent
n. someone who plays against you in a game or fight. It can also mean a person who disagrees with your ideas or plans.
n. a person who competes against another in a contest, game, or argument. Often used to describe someone who actively resists or disagrees with a specific policy or proposal.
He shook hands with his opponent after the match.
The leading candidate faced a tough challenge from her political opponent during the televised debate.
While the senator is a fierce opponent of the new tax law, he remains open to compromise if the environmental clauses are strengthened.
Usage
Often takes the preposition 'of' when describing opposition to an idea or policy.