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.
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?