The Oxford Thesaurus An A-Z Dictionary of Synonyms - challenge v.

1) question, dispute, defy, object to, take exception to, contest, doubt, call into doubt, call into or to question, impugn: I challenge the validity of your accusation. 2) invite, dare, summon, call out, provoke: The duke was challenged to a duel. 3) brave, dare, confront, defy, contest: We could challenge criticism with an easy confidence. --n. 4) question, dispute, doubt: His opinions are open to challenge. 5) invitation, dare, summons, provocation, confrontation, defiance; ultimatum: An older opponent might not have issued such a challenge. 6) problem, demand, stimulation, trial, test: Are you sure that Mr Wilson will be able to meet the challenge of the new position?