noun, verb, -lenged, -leng⋅ing, adjective | 1. | a call or summons to engage in any contest, as of skill, strength, etc. |
| 2. | something that by its nature or character serves as a call to battle, contest, special effort, etc.: Space exploration offers a challenge to humankind. |
| 3. | a call to fight, as a battle, a duel, etc. |
| 4. | a demand to explain, justify, etc.: a challenge to the treasurer to itemize expenditures. |
| 5. | difficulty in a job or undertaking that is stimulating to one engaged in it. |
| 6. | Military. the demand of a sentry for identification or a countersign. |
| 7. | 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. |
| 8. | the assertion that a vote is invalid or that a voter is not legally qualified. |
| 9. | Biology. the process of inducing or assessing physiological or immunological activity by exposing an organism to a specific substance. |
| 10. | Hunting. the crying of a hound on finding a scent. |
| 11. | to summon to a contest of skill, strength, etc. |
| 12. | to take exception to; call in question: to challenge the wisdom of a procedure. |
| 13. | to demand as something due or rightful. |
| 14. | Military. to halt and demand identification or countersign from. |
| 15. | Law. to take formal exception to (a juror or jury). |
| 16. | to have a claim to; invite; arouse; stimulate: a matter which challenges attention. |
| 17. | to assert that (a vote) is invalid. |
| 18. | to assert that (a voter) is not qualified to vote. |
| 19. | to expose an organism to a specific substance in order to assess its physiological or immunological activity. |
| 20. | Archaic. to lay claim to. |
| 21. | to make or issue a challenge. |
| 22. | Hunting. (of hounds) to cry or give tongue on picking up the scent. |
| 23. | 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. |