n.1. a. One who tells or plays jokes.
b. An insolent person who seeks to make a show of cleverness.
c. Informal An annoying or inept person: Some joker is blocking my driveway.
2. Games A playing card, usually printed with a picture of a jester, used in certain games as the highest-ranking card or as a wild card.
3. A clause that is included in a legislative bill or a contract in order to render the bill or contract inoperative or oppressive in some respect while appearing to be innocuous until the harm has been done.
4. An unforeseen but important difficulty, fact, or circumstance.
5. A deceptive means of getting the better of someone.