challenging

To invite (someone) to take part in a competition.

“We challenged the boys next door to a game of football.”

To dare (someone).

To dispute (something).

“to challenge the accuracy of a statement or of a quotation”

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).

“The sentinel challenged us with "Who goes there?"”

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.

The act of making a challenge.

Difficult, hard to do.