Joker

n. 1. One who makes jokes or jests. [ 1913 Webster ]

2. (Card Playing) See Best bower, under 2d Bower. [ 1913 Webster ]

3. (Card Playing) An extra card usually included in a deck of playing cards, having the same design as the others on the back, but on the face having a picture of a jester. It is not included in the deck used in most games, but in certain games may be included and then takes on a special value, such as the highest-valued card, or a wild card. [ PJC ]

4. A clause placed in a document, such as a contract or a piece of legislation, not itself appearing significant, but in a subtle way substantially changing the effect of the document. [ PJC ]

5. Hence: Any fact or condition which is unknown or not apparent, which reverses an apparently advantageous position; a kicker. [ PJC ]

6. A person; a fellow; a chap; -- usually used in a mildly disparaging sense; as, who's the joker who left the ice cream on the table?. [ PJC ]