Definition of: joker

(jō′kər) noun
1. One who jokes.
2. In certain card games, as euchre, an extra card that counts as the highest trump, or, in poker, as any card the holder names.
3. U.S. An ambiguous or inconspicuous clause, inserted in a legislative bill to render it ineffectual or cause it to serve some purpose other than the original intention of the bill.
4. Any hidden device or ruse used for purposes of trickery or deception.