a call or summons to engage in any contest, as of skill, strength, etc.

something that by its nature or character serves as a call to battle, contest, special effort, etc.

Space exploration offers a challenge to humankind.

a call to fight, as a battle, a duel, etc.

a demand to explain, justify, etc.

a challenge to the treasurer to itemize expenditures.

difficulty in a job or undertaking that is stimulating to one engaged in it.

Military . the demand of a sentry for identification or a countersign.

Law . a formal objection to the qualifications of a particular juror, to his or her serving, or to the legality of an entire jury. Compare peremptory challenge .

the assertion that a vote is invalid or that a voter is not legally qualified.

Biology . the process of inducing or assessing physiological or immunological activity by exposing an organism to a specific substance.

Hunting . the crying of a hound on finding a scent.

to summon to a contest of skill, strength, etc.

to take exception to; call in question

to challenge the wisdom of a procedure.

to demand as something due or rightful.

Military . to halt and demand identification or countersign from.

Law . to take formal exception to (a juror or jury).

to have a claim to; invite; arouse; stimulate

a matter which challenges attention.

to assert that (a vote) is invalid.

to assert that (a voter) is not qualified to vote.

to expose an organism to a specific substance in order to assess its physiological or immunological activity.

Archaic . to lay claim to.

to make or issue a challenge.

Hunting . (of hounds) to cry or give tongue on picking up the scent.

donated or given by a private, corporate, or government benefactor on condition that the recipient raise an additional specified amount from the public

a challenge grant.

noun

agree , answer , decide , win

verb

agreement , answer , decision , victory

noun

claiming , confrontation , dare , defiance , demanding , demur , interrogation , objection , protest , provocation , remonstrance , summons to contest , test , threat , trial , ultimatum , exception , expostulation , protestation , remonstration , squawk

verb

accost , arouse , ask for , assert , beard , brave , call for , call out , claim , confront , cross , dare , defy , demand , denounce , exact , face down , face off , face the music * , fly in the face of , hang in , impeach , impose , impugn , inquire , insist upon , investigate , invite competition , make a point of , make a stand , object to , provoke , query , reclaim , require , search out , stand up to , stick it out , stimulate , summon , tax , test , throw down the gauntlet * , try , vindicate , face , front , approach , approximate , border on , verge on , demur , except , expostulate , inveigh , protest , remonstrate , buck , dispute , oppose , resist , traverse , accuse , appeal , arraign , brave.--n. defiance , call , censure , charge , controvert , exception , forbid , invite , objection , question , reproach , slap , stump , summons