A funny person.
An unspecified, vaguely disreputable person.
A friendly unit that acts as a suspected hostile unit in a military excercise.
A jester.
A person who makes jokes.
A clause in a contract that undermines its apparent provisions.
A man.
A playing card that features a picture of a joker (that is, a jester) and that may be used as a wild card in some card games.