late 14c., jakke "a mechanical device," from the name
Jack. Used by 14c. for "any common fellow" (mid-14c.), and thereafter extended to various appliances replacing servants (1570s). Used generically of men (jack-of-all-trades, 1610s), male animals (1620s, see jackass, jackdaw,
etc.), and male personifications (1520s, e.g. Jack Frost). The jack in a pack of playing cards (1670s) is in Ger. Bauer "peasant." Jackhammer is from 1930. Jack shit "nothing at all" is 1970s southern U.S. student slang. The jack of
Union Jack is a nautical term for a small flag at the bow of a ship (1630s).
