a challenge

to invite or summon (someone to do something, esp to take part in a contest)

to call (something) into question; dispute

to make demands on; stimulate

to order (a person) to halt and be identified or to give a password

to make formal objection to (a juror or jury)

to lay claim to (attention, etc)

(of a hound) to cry out on first encountering the scent of a quarry

to inject (an experimental animal immunized with a test substance) with disease microorganisms to test for immunity to the disease

a call to engage in a fight, argument, or contest

a questioning of a statement or fact; a demand for justification or explanation

a demanding or stimulating situation, career, object, etc

a demand by a sentry, watchman, etc, for identification or a password

an assertion that a person is not entitled to vote or that a vote is invalid

a formal objection to a person selected to serve on a jury (challenge to the polls) or to the whole body of jurors (challenge to the array)