Joker
Part of speech: noun
Definition: A person who makes jokes. A funny person A jester. 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. An unspecified, vaguely disreputable person. A man.
Example sentence: The greatest villain of all time is The Joker - he always has been, and I don't know anyone who's not going to have Heath Ledger's performance burnt into their brains for the rest of their lives.
Clown
Part of speech: noun
Definition: A performance artist often associated with a circus and typically characterised by bright, oversized clothing, a red nose, face paint, and a brightly colored wig and who performs slapstick.A person who acts in a silly fashion.
Part of speech: verb
Definition: (also clown about (British) or clown around) To act in a silly fashion.