Source : Webster's Revised Unabridged Dictionary (1913)

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.