challenger ['tʃælɪndʒə(r)]

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附加级

n.挑战者；夺标者

the official challenger for the world championship title 世界冠军头衔的正式挑战者
The judges gave the nod to the winning challenger. 裁判们对挑战者的胜利给予确认。来自《简明英汉词典》