Merriam-Webster's Collegiate® Dictionary, 11th Edition
JACKET
I. noun
Etymology: Middle English jaket, from Anglo-French jackés, plural, diminutive of Middle French jaque short jacket, from jacques peasant, from the name Jacques James
Date: 15th century
1. a garment for the upper body usually having a front opening, collar, lapels, sleeves, and pockets, something worn or fastened around the body but not for use as clothing,
2. a. the natural covering of an animal, the fur or wool of a mammal, the skin of a potato, an outer covering or casing: as, a. a thermally nonconducting cover, a covering that encloses an intermediate space through which a temperature-controlling fluid circulates, a tough cold-worked metal casing that forms the outer shell of a built-up bullet, b. a wrapper or open envelope for a document, an envelope for enclosing registered mail during delivery from one post office to another, c. a detachable protective cover for a book, a paper or cardboard envelope for a phonograph record, jacketless adjective
II. transitive verb
Date: 1856
to put a jacket on ; enclose in or with a jacket