The Oxford Thesaurus An A-Z Dictionary of Synonyms - joker n.

1) jokester, comedian, comedienne, funny man, humorist, jester, comic, clown, wag, wit, punster, droll, zany, merry andrew, buffoon, trickster, prankster, Colloq card, gagster, gag man, kidder: Give him a drink and a funny hat and Roger thinks he's the greatest joker in the world. 2) US catch, hitch, snag, drawback, trap, twist, pitfall, fine or small print, Colloq catch-22, no-win situation, Taboo nigger in the woodpile: The joker is that whoever treats the patients catches the disease.