jacket (n.)

late 14c., jakke "a mechanical device," from the masc. name Jack. The proper name was used in Middle English for "any common fellow," and thereafter extended to various appliances which do the work of common servants (1570s). Also used generically of male animals (1620s, see jackass, jackdaw, etc.).

As a portable contrivance for raising weight by force from below, 1703. As the name of a device for pulling off boots from 1670s. The jack in a pack of playing cards (1670s) is in German Bauer "peasant." Slang meaning "money" is by 1890 (in earlier slang it meant "a small coin"). Jack-towel, one sewn together at the ends round a roller, is from 1795. The jack of Union Jack is a nautical term for "small flag at the bow of a ship" (1630s) and perhaps is from the word's secondary sense of "smaller than normal size."

"French peasantry," 1520s, from French jacquerie "peasants or villeins collectively" (15c.), from Jacques, the proper name, which is used as Jack is used in English, in the sense of "any common fellow." So it also means "the rising of the northern French peasants against the nobles in 1357-8," from a French usage. Etymologically, Jacques is from Late Latin Iacobus (see Jacob).