What is the meaning of the word "jack"?

Definitions:

A device for lifting heavy objects, especially on e for raising the axle of a motor vehicle off the ground so that a wheel can be checked or the underside inspected. NOUN
- Finally, lower the jack so the wheel is back down on the road.
- You need a jack in order to change a tire.
A plug used in a jack socket, consisting of a shaft used to make a connection that transmits a signal, typically used in sound equipment. NOUN
- An earphone jack includes an insulating housing and conductive first, second and third contact members.
A small version of a national flag flown at the bow of a vessel in harbor to indicate its nationality. NOUN
- The union jack is raised after the national ensign and lowered before the national ensign at evening colors.
A socket designed to receive a jack plug. NOUN
- Plug a tape recorder into the headphone jack of the computer with a double plug cord.
Slang for 'nothing'. NOUN
- I know 'jack' about fashion but I know what I like to wear.