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Synonyms for Champion (same or very similar meaning)

WordNet sense 1 (a person who backs a politician or a team etc.):
admirer, booster, friend, protagonist, supporter

WordNet sense 2 (someone who has won first place in a competition):
champ, title-holder

WordNet sense 3 (someone who fights for a cause):
fighter, hero, paladin

WordNet sense 4 (someone who is dazzlingly skilled in any field):
ace, adept, genius, hotshot, maven, sensation, star, superstar, virtuoso, whiz, whizz, wiz, wizard, mavin, adept

WordNet sense 5 (protect or fight for as a champion):

WordNet sense 6 (holding first place in a contest):

From the ODE community, based on WordNetadd/edit