a person who takes part in a contest or competition.

a person who contests the results of an election.

Law . the party who, in proceedings in the probate court, contests the validity of a will.

noun

adversary , antagonist , aspirant , battler , candidate , challenger , combatant , contender , contester , dark horse * , disputant , entrant , favorite , hopeful , member , participant , player , rival , scrapper , team member , warrior , competition , corrival , opponent , competitor , defendant , enterer , entry , finalist , prospect