Joker (musician) definition

(1) A playing card that is usually printed with a picture of a jester

(2) An inconspicuous clause in a document or bill that affects its meaning in a way that is not immediately apparent

"When I demanded my money he showed me the joker in the contract"

(3) A person who enjoys telling or playing jokes

(4) A person who does something thoughtless or annoying

"Some joker is blocking the driveway"