challenger

noun5

1. •
   One who challenges.

   • [C]ertainly there is no true orator who is not a hero. […] He is challenger and must answer all comers. — 1876
2. •
   One who confronts or opposes; a confronter, an opposer.

   • challengers of traditional attitudes
3. •
   One who plays against the current champion of a contest or game in hopes of winning and becoming the new champion.

   • The champion hopes to defeat his new challenger in the game to remain undefeated.
   • One child stood as king of the hill, and tried to withstand the pushes and shoves of his challengers.
4. •
   [before a noun] Often in the form Challenger: a match, tournament, or tour of the second-highest tier organized by the Association of Tennis Professionals.
5. •
   (no longer used) One who brings a legal claim; a claimant, a plaintiff; also, one who accuses; an accuser.

   • Novv vvhen they vvere come before Appius, sitting judicially upon his tribunall seate, the plaintife or challenger aforesaid, declareth against her, […] — 1600

noun1

1. •
   A steam locomotive of the 4-6-6-4 wheel arrangement.