The act of making a challenge.
To invite (someone) to take part in a competition.
To dare (someone).
To dispute (something).
To make a formal objection to a juror.
To claim as due; to demand as a right.
To censure; to blame.
To question or demand the countersign from (one who attempts to pass the lines).
To object to the reception of the vote of, e.g. on the ground that the person is not qualified as a voter.
To take (a final exam) in order to get credit for a course without taking it.
Difficult, hard to do.