A device for lifting heavy objects, especially a car, off the ground. He used a jack to lift the car and change the tire.
A playing card bearing the picture of a soldier or servant, ranking below a queen and above a ten. She drew a jack of hearts from the deck.
A small flag flown at the bow of a ship, typically symbolizing nationality. The ship raised its jack as it entered the harbor.
A socket designed to receive a plug, especially one for audio or video equipment. He plugged his headphones into the jack on his computer.
The farmer owned a jack and a jenny to help with farm work.
Nothing at all; anything (slang, chiefly used in negative constructions). He doesn't know jack about computers.
A generic or informal term for a man, worker, or fellow, especially of the working class (often in set phrases and historical use). Every man jack of them stood firm in the face of danger.