challenge

(noun) a demanding or stimulating situation. Example: "They reacted irrationally to the challenge of russian power."

(noun) a call to engage in a contest or fight.

(noun) questioning a statement and demanding an explanation. Example: "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 demand by a sentry for a password or identification.

(verb) take exception to. Synonyms: dispute, gainsay. Example: "She challenged his claims."

(verb) issue a challenge to. Example: "Fischer challenged spassky to a match."

(verb) ask for identification. Example: "The illegal immigrant was challenged by the border guard."

(verb) raise a formal objection in a court of law. Synonyms: take exception.