What does JACK mean?

noun

1. a small worthless amount“you don't know jack”
2. someone who works with their hands; someone engaged in manual labor
3. immense East Indian fruit resembling breadfruit; it contains an edible pulp and nutritious seeds that are commonly roasted
4. a small ball at which players aim in lawn bowling
5. an electrical device consisting of a connector socket designed for the insertion of a plug
6. game equipment consisting of one of several small six-pointed metal pieces that are picked up while bouncing a ball in the game of jacks
7. small flag indicating a ship's nationality
8. one of four face cards in a deck bearing a picture of a young prince