Definition of "Challenge" :

noun: a demand by a sentry for a password or identification

noun: questioning a statement and demanding an explanation

"His challenge of the assumption that Japan is still our enemy."

noun: a formal objection to the selection of a particular person as a juror

noun: a call to engage in a contest or fight

noun: a demanding or stimulating situation

"They reacted irrationally to the challenge of Russian power."

verb: raise a formal objection in a court of law

verb: ask for identification

"The illegal immigrant was challenged by the border guard."

verb: issue a challenge to

"Fischer challenged Spassky to a match."

verb: take exception to

"She challenged his claims."