noun
rival candidate; opponent
Used in elections or competitions to refer to a competing candidate or person. Often implies a strong challenger.
彼は強力な対抗馬として選挙戦に臨んだ。
He entered the election campaign as a strong rival candidate.
そのレースでは、対抗馬が最後の直線で抜け出した。
In that race, the rival horse pulled ahead on the final straight.
Compound of 対抗 (opposition) and 馬 (horse), originally a horse racing term for a rival horse, later extended to political and competitive contexts.