joker

1. (slang) A funny person.slang

2. (figurative) Something kept in reserve that can be used to gain an advantage; a trump card.Examples: "Rebus decided to use their joker. 'Mr Lintz made a phone call to this office. He was talking for over twenty minutes.'"; "Tash Wilson played her 'joker' , pulling her chair so close our legs were almost touching. 'Hey, Chris, do you want to go out sometime? All you've got to do is say the word.'"; "The director made me understand that my bubble of stardom could burst just as soon as it had been inflated if I didn't watch my attitude. Then he used his joker. I had an understudy so if I messed up or tried to create a scene, I would be summarily replaced."figuratively

3. (New Zealand, colloquial) A man.New-Zealandcolloquial

4. (military) A friendly unit that acts as a suspected hostile unit in a military excercise.Examples: "Joker - A friendly track or contact acting as a "suspect" track for exercise purposes only. (STANAG 1241)"

5. (chess) A fairy chess piece that moves like the last piece that was moved by the opponent.Examples: "The problem is that it would be difficult to use a joker offensively since you could never know how it was going to move, meaning it’d be most useful setting it up for potential queen/rook captures to disincentivize your opponent from moving those pieces."