<p><strong>Noun</strong></p><ul><li>a call or summons to engage in any contest, as of skill, strength, etc.</li><li>something that by its nature or character serves as a call to battle, contest, special effort, etc.</li><li>a call to fight, as a battle, a duel, etc.</li><li>a demand to explain, justify, etc.</li><li>difficulty in a job or undertaking that is stimulating to one engaged in it</li><li>the demand of a sentry for identification or a countersign</li><li>a formal objection to the qualifications of a particular juror, to that juror serving, or to the legality of an entire jury</li><li>the assertion that a vote is invalid or that a voter is not legally qualified</li><li>the process of inducing or assessing physiological or immunological activity by exposing an organism to a specific substance</li><li>the crying of a hound on finding a scent</li></ul><p><strong>Verb</strong></p><ul><li>to summon to a contest of skill, strength, etc.</li></ul><p><strong>Synonyms</strong></p><ul><li>invite</li><li>bid</li><li>dare</li></ul><p><strong>Examples</strong></p><ul><li>to take exception to; call in question: to challenge the wisdom of a procedure</li><li>to demand as something due or rightful</li><li>to halt and demand identification or countersign from</li><li>to take formal exception to (a juror or jury)</li><li>to assert that (a vote) is invalid</li><li>to assert that (a voter) is not qualified to vote</li><li>to expose an organism to a specific substance in order to assess its physiological or immunological activity</li></ul><p><strong>Adjective</strong></p><ul><li>donated or given by a private, corporate, or government benefactor on condition that the recipient raise an additional specified amount from the public</li></ul>