Source : Webster's Revised Unabridged Dictionary (1913)

   {Jack rabbit} (Zo["o]l.), any one of several species of large
      American hares, having very large ears and long legs. The
      California species ({Lepus Californicus}), and that of
      Texas and New Mexico ({L. callotis}), have the tail black
      above, and the ears black at the tip. They do not become
      white in winter. The more northern prairie hare ({L.
      campestris}) has the upper side of the tail white, and in
      winter its fur becomes nearly white.

   {Jack rafter} (Arch.), in England, one of the shorter rafters
      used in constructing a hip or valley roof; in the United
      States, any secondary roof timber, as the common rafters
      resting on purlins in a trussed roof; also, one of the
      pieces simulating extended rafters, used under the eaves
      in some styles of building.

   {Jack salmon} (Zo["o]l.), the wall-eyed pike, or glasseye.

   {Jack sauce}, an impudent fellow. [Colloq. & Obs.]

   {Jack shaft} (Mach.), the first intermediate shaft, in a
      factory or mill, which receives power, through belts or
      gearing, from a prime mover, and transmits it, by the same
      means, to other intermediate shafts or to a line shaft.

   {Jack sinker} (Knitting Mach.), a thin iron plate operated by
      the jack to depress the loop of thread between two
      needles.

   {Jack snipe}. (Zo["o]l.) See in the Vocabulary.

   {Jack staff} (Naut.), a staff fixed on the bowsprit cap, upon
      which the jack is hoisted.

   {Jack timber} (Arch.), any timber, as a rafter, rib, or
      studding, which, being intercepted, is shorter than the
      others.

   {Jack towel}, a towel hung on a roller for common use.

   {Jack truss} (Arch.), in a hip roof, a minor truss used where
      the roof has not its full section.

   {Jack tree}. (Bot.) See 1st {Jack}, n.

   {Jack yard} (Naut.), a short spar to extend a topsail beyond
      the gaff.

   {Blue jack}, blue vitriol; sulphate of copper.

   {Hydraulic jack}, a jack used for lifting, pulling, or
      forcing, consisting of a compact portable hydrostatic
      press, with its pump and a reservoir containing a supply
      of liquid, as oil.

   {Jack-at-a-pinch}.
       (a) One called upon to take the place of another in an
           emergency.
       (b) An itinerant parson who conducts an occasional
           service for a fee.

   {Jack-at-all-trades}, one who can turn his hand to any kind
      of work.

   {Jack-by-the-hedge} (Bot.), a plant of the genus {Erysimum}
      ({E. alliaria}, or {Alliaria officinalis}), which grows
      under hedges. It bears a white flower and has a taste not
      unlike garlic. Called also, in England, {sauce-alone}.
      --Eng. Cyc.

   {Jack-in-a-box}.
       (a) (Bot.) A tropical tree ({Hernandia sonora}), which
           bears a drupe that rattles when dry in the inflated
           calyx.
       (b) A child's toy, consisting of a box, out of which,
           when the lid is raised, a figure springs.
       (c) (Mech.) An epicyclic train of bevel gears for
           transmitting rotary motion to two parts in such a
           manner that their relative rotation may be variable;
           applied to driving the wheels of tricycles, road
           locomotives, and to cotton machinery, etc.; an
           equation box; a jack frame; -- called also
           {compensating gearing}.
       (d) A large wooden screw turning in a nut attached to the
           crosspiece of a rude press.

   {Jack-in-office}, an insolent fellow in authority. --Wolcott.

   {Jack-in-the-bush} (Bot.), a tropical shrub with red fruit
      ({Cordia Cylindrostachya}).

   {Jack-in-the-green}, a chimney sweep inclosed in a framework
      of boughs, carried in Mayday processions.

   {Jack-in-the-pulpit} (Bot.), the American plant {Aris[ae]ma
      triphyllum}, or Indian turnip, in which the upright spadix
      is inclosed.

   {Jack-of-the-buttery} (Bot.), the stonecrop ({Sedum acre}).
      

   {Jack-of-the-clock}, a figure, usually of a man, on old
      clocks, which struck the time on the bell.

   {Jack-on-both-sides}, one who is or tries to be neutral.

   {Jack-out-of-office}, one who has been in office and is
      turned out. --Shak.

   {Jack the Giant Killer}, the hero of a well-known nursery
      story.

   {Jack-with-a-lantern}, {Jack-o'-lantern}.
       (a) An ignis fatuus; a will-o'-the-wisp. ``[Newspaper
           speculations] supplying so many more jack-o'-lanterns
           to the future historian.'' --Lowell.
       (b) A lantern made of a pumpkin so prepared as to show in
           illumination the features of a human face, etc.

   {Yellow Jack} (Naut.), the yellow fever; also, the quarantine
      flag. See {Yellow flag}, under {Flag}.

Hydraulic \Hy*drau"lic\, a. [F. hydraulique, L. hydraulicus, fr.
   Gr. ?, ?, a water organ; "y`dwr water + ? flute, pipe. See
   {Hydra}.]
   Of or pertaining to hydraulics, or to fluids in motion;
   conveying, or acting by, water; as, an hydraulic clock,
   crane, or dock.

   {Hydraulic accumulator}, an accumulator for hydraulic
      machinery of any kind. See {Accumulator}, 2.

   {Hydraulic brake}, a cataract. See {Cataract}, 3.

   {Hydraulic cement}, a cement or mortar made of hydraulic
      lime, which will harden under water.

   {Hydraulic elevator}, a lift operated by the weight or
      pressure of water.

   {Hydraulic jack}. See under {Jack}.

   {Hydraulic lime}, quicklime obtained from hydraulic
      limestone, and used for cementing under water, etc.

   {Hydraulic limestone}, a limestone which contains some clay,
      and which yields a quicklime that will set, or form a
      firm, strong mass, under water.

   {Hydraulic main} (Gas Works), a horizontal pipe containing
      water at the bottom into which the ends of the pipes from
      the retorts dip, for passing the gas through water in
      order to remove ammonia.

   {Hydraulic mining}, a system of mining in which the force of
      a jet of water is used to wash down a bank of gold-bearing
      gravel or earth. [Pacific Coast]

   {Hydraulic press}, a hydrostatic press. See under
      {Hydrostatic}.

   {Hydraulic propeller}, a device for propelling ships by means
      of a stream of water ejected under water rearward from the
      ship.

   {Hydraulic ram}, a machine for raising water by means of the
      energy of the moving water of which a portion is to be
      raised. When the rush of water through the main pipe d
      shuts the valve at a, the momentum of the current thus
      suddenly checked forces part of it into the air chamber b,
      and up the pipe c, its return being prevented by a valve
      at the entrance to the air chamber, while the dropping of
      the valve a by its own weight allows another rush through
      the main pipe, and so on alternately.

   {Hydraulic valve}. (Mach.)
   (a) A valve for regulating the distribution of water in the
       cylinders of hydraulic elevators, cranes, etc.
   (b) (Gas Works) An inverted cup with a partition dipping into
       water, for opening or closing communication between two
       gas mains, the open ends of which protrude about the
       water.