opponent
/əˈpəʊnənt/noun
1- someone who competes with or fights another in a contest, game, or argument; a rival or adversary对手; 敌手：
he beat his Republican opponent by a landslide margin.
他以绝对多数击败了他的共和党对手。
1.1
- a person who disagrees with or resists a proposal or practice反对者：
an opponent of the economic reforms.
经济改革的反对者。
词源
late 16th cent. (denoting a person opening an academic debate by proposing objections to a philosophical or religious thesis)： from Latin opponent- 'setting against', from the verb opponere, from ob- 'against' + ponere 'place'.