Source : Webster's Revised Unabridged Dictionary (1913)

Jack \Jack\ (j[a^]k), n. [Pg. jaca, Malayalam, tsjaka.] (Bot.)
   A large tree, the {Artocarpus integrifolia}, common in the
   East Indies, closely allied to the breadfruit, from which it
   differs in having its leaves entire. The fruit is of great
   size, weighing from thirty to forty pounds, and through its
   soft fibrous matter are scattered the seeds, which are
   roasted and eaten. The wood is of a yellow color, fine grain,
   and rather heavy, and is much used in cabinetwork. It is also
   used for dyeing a brilliant yellow. [Written also {jak}.]

Jack \Jack\, n. [F. Jacques James, L. Jacobus, Gr. ?, Heb. Ya
   'aq[=o]b Jacob; prop., seizing by the heel; hence, a
   supplanter. Cf. {Jacobite}, {Jockey}.]
   1. A familiar nickname of, or substitute for, John.

            You are John Rugby, and you are Jack Rugby. --Shak.

   2. An impertinent or silly fellow; a simpleton; a boor; a
      clown; also, a servant; a rustic. ``Jack fool.''
      --Chaucer.

            Since every Jack became a gentleman, There 's many a
            gentle person made a Jack.            --Shak.

   3. A popular colloquial name for a sailor; -- called also
      {Jack tar}, and {Jack afloat}.

   4. A mechanical contrivance, an auxiliary machine, or a
      subordinate part of a machine, rendering convenient
      service, and often supplying the place of a boy or
      attendant who was commonly called Jack; as:
      (a) A device to pull off boots.
      (b) A sawhorse or sawbuck.
      (c) A machine or contrivance for turning a spit; a smoke
          jack, or kitchen jack.
      (b) (Mining) A wooden wedge for separating rocks rent by
          blasting.
      (e) (Knitting Machine) A lever for depressing the sinkers
          which push the loops down on the needles.
      (f) (Warping Machine) A grating to separate and guide the
          threads; a heck box.
      (g) (Spinning) A machine for twisting the sliver as it
          leaves the carding machine.
      (h) A compact, portable machine for planing metal.
      (i) A machine for slicking or pebbling leather.
      (k) A system of gearing driven by a horse power, for
          multiplying speed.
      (l) A hood or other device placed over a chimney or vent
          pipe, to prevent a back draught.
      (m) In the harpsichord, an intermediate piece
          communicating the action of the key to the quill; --
          called also {hopper}.
      (n) In hunting, the pan or frame holding the fuel of the
          torch used to attract game at night; also, the light
          itself. --C. Hallock.

   5. A portable machine variously constructed, for exerting
      great pressure, or lifting or moving a heavy body through
      a small distance. It consists of a lever, screw, rack and
      pinion, hydraulic press, or any simple combination of
      mechanical powers, working in a compact pedestal or
      support and operated by a lever, crank, capstan bar, etc.
      The name is often given to a jackscrew, which is a kind of
      jack.

   6. The small bowl used as a mark in the game of bowls.
      --Shak.

            Like an uninstructed bowler who thinks to attain the
            jack by delivering his bowl straight forward upon
            it.                                   --Sir W.
                                                  Scott.

   7. The male of certain animals, as of the ass.

   8. (Zo["o]l.)
      (a) A young pike; a pickerel.
      (b) The jurel.
      (c) A large, California rock fish ({Sebastodes
          paucispinus}); -- called also {boccaccio}, and
          {m['e]rou}.
      (d) The wall-eyed pike.

   9. A drinking measure holding half a pint; also, one holding
      a quarter of a pint. [Prov. Eng.] --Halliwell.

   10. (Naut.)
       (a) A flag, containing only the union, without the fly,
           usually hoisted on a jack staff at the bowsprit cap;
           -- called also {union jack}. The American jack is a
           small blue flag, with a star for each State.
       (b) A bar of iron athwart ships at a topgallant masthead,
           to support a royal mast, and give spread to the royal
           shrouds; -- called also {jack crosstree}. --R. H.
           Dana, Jr.

Jack \Jack\, v. t.
   To move or lift, as a house, by means of a jack or jacks. See
   2d {Jack}, n., 5.

Jack \Jack\, n. [F. jaque, jacque, perh. from the proper name
   Jacques. Cf. {Jacquerie}.]
   A coarse and cheap medi[ae]val coat of defense, esp. one made
   of leather.

         Their horsemen are with jacks for most part clad. --Sir
                                                  J. Harrington.

Jack \Jack\, n. [Named from its resemblance to a jack boot.]
   A pitcher or can of waxed leather; -- called also {black
   jack}. [Obs.] --Dryden.

Jack \Jack\, v. i.
   To hunt game at night by means of a jack. See 2d {Jack}, n.,
   4, n.

Source : WordNet®

jack
     v 1: lift with a special device; "jack up the car so you can
          change the tire" [syn: {jack up}]
     2: hunt with a jacklight [syn: {jacklight}]

jack
     n 1: a small worthless amount; "you don't know jack" [syn: {diddly-squat},
           {diddlysquat}, {diddly-shit}, {diddlyshit}, {diddly}, {diddley},
           {squat}, {shit}]
     2: a man who serves as a sailor [syn: {mariner}, {seaman}, {tar},
         {Jack-tar}, {old salt}, {seafarer}, {gob}, {sea dog}]
     3: someone who works with their hands; someone engaged in
        manual labor [syn: {laborer}, {manual laborer}, {labourer}]
     4: immense East Indian fruit resembling breadfruit of; its
        seeds are commonly roasted [syn: {jackfruit}, {jak}]
     5: an electrical device consisting of a connector socket
        designed for the insertion of a plug
     6: game equipment consisting of one of several small objects
        picked up while bouncing a ball in the game of jacks
     7: small flag indicating a ship's nationality
     8: one of four face cards in a deck bearing a picture of a
        young prince [syn: {knave}]
     9: tool for exerting pressure or lifting
     10: any of several fast-swimming predacious fishes of tropical
         to warm-temperate seas
     11: male donkey [syn: {jackass}]