n. & v.
n. 1 a device for lifting heavy objects, esp. the axle of a vehicle off the ground while changing a wheel etc. 2 a court-card with a picture of a man, esp. a soldier, page, or knave, etc. 3 a ship's flag, esp. one flown from the bow and showing nationality. 4 a device using a single plug to connect an electrical circuit. 5 a small white ball in bowls, at which the players aim. 6 a = JACKSTONE. b (in pl.) a game of jackstones. 7 (Jack) the familiar form of John esp. typifying the common man or the male of a species (I'm all right, Jack). 8 the figure of a man striking the bell on a clock. 9 sl. a detective; a policeman. 10 US sl. money. 11 = LUMBERJACK. 12 = STEEPLEJACK. 13 a device for turning a spit. 14 any of various marine perchlike fish of the family Carangidae, including the amberjack. 15 a device for plucking the string of a harpsichord etc., one being operated by each key.
v.tr. (usu. foll. by up) 1 raise with or as with a jack (in sense 1). 2 colloq. raise e.g. prices. every man jack each and every person. Jack Frost frost personified. jack in (or up) sl. abandon (an attempt etc.). jack-in-the-box a toy figure that springs out of a box when it is opened. jack-in-office a self-important minor official. jack of all trades a person who can do many different kinds of work. jack-o'-lantern 1 a will-o'-the wisp. 2 a lantern made esp. from a pumpkin with holes for facial features. jack plane a medium-sized plane for use in rough joinery. jack plug a plug for use with a jack (see sense 4 of n.). Jack tar a sailor. on one's jack (or Jack Jones) sl. alone; on one's own.
[ ME Iakke, a pet-name for John, erron. assoc. with F Jacques James ]