ETYM French jaquette, dim. of jaque. Related to Jack.
1. A short coat.
2. An outer covering or casing.
3. The tough metal casing for certain kinds of ammunition.
Short coat, usually coming to the waist or hip, worn by both men and women. Jackets are worn in combination with skirts and trousers to form suits, or separately, both indoors and outdoors. They are both fashion and utilitarian garments.

See disk jacket.

1. To provide with a thermally non-conducting cover.
2. To put a jacket on.