n a person who does something thoughtless or annoying
some joker is blocking the driveway
n an inconspicuous clause in a document or bill that affects its meaning in a way that is not immediately apparent
when I demanded my money he showed me the joker in the contract
n a playing card that is usually printed with a picture of a jester
n French nuclear physicist who was Marie Curie's assistant and who worked with Marie Curie's daughter who he married (taking the name Joliot-Curie); he and his wife discovered how to synthesize new radioactive elements (1900-1958)