An "election opponent" refers to a person or political party who is competing against someone in an election. They are the opposing candidate who is running for the same position and aiming to win the election themselves. Full definition
Sometimes there isn't even a general election opponent on the ballot. (gothamgazette.com)
He's already gone negative in radio and TV ads against his primary opponents, his potential general election opponent and the president. (nystateofpolitics.com)
His special election opponents Cordell Cleare and Marvin Holland are seen as the strongest challengers. (shakingnews.com)