joker (Noun) — A person who enjoys telling or playing jokes.
joker (Noun) — A person who does something thoughtless or annoying. ex. "some joker is blocking the driveway"
joker (Noun) — An inconspicuous clause in a document or bill that affects its meaning in a way that is not immediately apparent. ex. "when I demanded my money he showed me the joker in the contract"
joker (Noun) — A playing card that is usually printed with a picture of a jester.