to invite or call to fight or compete
to defy (somebody) boldly or dare them to do a specified thing
to invite or call (somebody) to fight or compete
to dispute (something), esp as being unjust, invalid, or outmoded
new data that challenges old assumptions
to question formally the legality or legal qualifications of (e.g. a juror)
to order (somebody) to halt and provide proof of identity
to test the skill of (somebody) in a stimulating way
to administer infective material to (an organism) in order to ascertain whether experimental immunization has been effective