The Collaborative International Dictionary of English v.0.48:

Champion \Cham"pi*on\ (ch[a^]m"p[i^]*[u^]n), n. [F. champion,
   fr. LL.campio, of German origin; cf. OHG. chempho, chemphio,
   fighter, champf, G. kampf, contest; perh. influenced by L.
   campus field, taken in the sense of "field of battle."]
   1. One who engages in any contest; especially one who in
      ancient times contended in single combat in behalf of
      another's honor or rights; or one who now acts or speaks
      in behalf of a person or a cause; a defender; an advocate;
      a hero.
      [1913 Webster]

            A stouter champion never handled sword. --Shak.
      [1913 Webster]

            Champions of law and liberty.         --Fisher Ames.
      [1913 Webster]

   2. One who by defeating all rivals, has obtained an
      acknowledged supremacy in any branch of athletics or game
      of skill, and is ready to contend with any rival; as, the
      champion of England.
      [1913 Webster]

   Note: Champion is used attributively in the sense of
         surpassing all competitors; overmastering; as, champion
         pugilist; champion chess player.

   Syn: Leader; chieftain; combatant; hero; warrior; defender;
        protector.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Champion \Cham"pi*on\, v. t. [imp. & p. p. Championed; p. pr.
   & vb. n. Championing.] [Obs.] --Shak.
   [1913 Webster]
   2. To furnish with a champion; to attend or defend as
      champion; to support or maintain; to protect.
      [1913 Webster]

            Championed or unchampioned, thou diest. --Sir W.
                                                  Scott.
      [1913 Webster]

WordNet (r) 3.0 (2006):

champion
    adj 1: holding first place in a contest; "a champion show dog";
           "a prizewinning wine" [syn: champion, prizewinning]
    n 1: someone who has won first place in a competition [syn:
         champion, champ, title-holder]
    2: someone who fights for a cause [syn: champion, fighter,
       hero, paladin]
    3: a person who backs a politician or a team etc.; "all their
       supporters came out for the game"; "they are friends of the
       library" [syn: supporter, protagonist, champion,
       admirer, booster, friend]
    4: someone who is dazzlingly skilled in any field [syn: ace,
       adept, champion, sensation, maven, mavin,
       virtuoso, genius, hotshot, star, superstar, whiz,
       whizz, wizard, wiz]
    v 1: protect or fight for as a champion [syn: champion,
         defend]