Source : Webster's Revised Unabridged Dictionary (1913)

Steam \Steam\, n. [OE. stem, steem, vapor, flame, AS. ste['a]m
   vapor, smoke, odor; akin to D. stoom steam, perhaps
   originally, a pillar, or something rising like a pillar; cf.
   Gr. ? to erect, ? a pillar, and E. stand.]
   1. The elastic, a["e]riform fluid into which water is
      converted when heated to the boiling points; water in the
      state of vapor.

   2. The mist formed by condensed vapor; visible vapor; -- so
      called in popular usage.

   3. Any exhalation. ``A steam og rich, distilled perfumes.''
      --Milton.

   {Dry steam}, steam which does not contain water held in
      suspension mechanically; -- sometimes applied to
      superheated steam.

   {Exhaust steam}. See under {Exhaust}.

   {High steam}, or {High-pressure steam}, steam of which the
      pressure greatly exceeds that of the atmosphere.

   {Low steam}, or {Low-pressure steam}, steam of which the
      pressure is less than, equal to, or not greatly above,
      that of the atmosphere.

   {Saturated steam}, steam at the temperature of the boiling
      point which corresponds to its pressure; -- sometimes also
      applied to {wet steam}.

   {Superheated steam}, steam heated to a temperature higher
      than the boiling point corresponding to its pressure. It
      can not exist in contact with water, nor contain water,
      and resembles a perfect gas; -- called also {surcharged
      steam}, {anhydrous steam}, and {steam gas}.

   {Wet steam}, steam which contains water held in suspension
      mechanically; -- called also {misty steam}.

   Note: Steam is often used adjectively, and in combination, to
         denote, produced by heat, or operated by power, derived
         from steam, in distinction from other sources of power;
         as in steam boiler or steam-boiler, steam dredger or
         steam-dredger, steam engine or steam-engine, steam
         heat, steam plow or steam-plow, etc.

   {Steam blower}.
      (a) A blower for producing a draught consisting of a jet
          or jets of steam in a chimney or under a fire.
      (b) A fan blower driven directly by a steam engine.

   {Steam boiler}, a boiler for producing steam. See {Boiler},
      3, and Note. In the illustration, the shell a of the
      boiler is partly in section, showing the tubes, or flues,
      which the hot gases, from the fire beneath the boiler,
      enter, after traversing the outside of the shell, and
      through which the gases are led to the smoke pipe d, which
      delivers them to the chimney; b is the manhole; c the
      dome; e the steam pipe; f the feed and blow-off pipe; g
      the safety value; hthe water gauge.

   {Steam car}, a car driven by steam power, or drawn by a
      locomotive.

   {Steam carriage}, a carriage upon wheels moved on common
      roads by steam.

   {Steam casing}. See {Steam jacket}, under {Jacket}.

   {Steam chest}, the box or chamber from which steam is
      distributed to the cylinder of a steam engine, steam pump,
      etc., and which usually contains one or more values; --
      called also {valve chest}, and {valve box}. See Illust. of
      {Slide valve}, under {Slide}.

   {Steam chimney}, an annular chamber around the chimney of a
      boiler furnace, for drying steam.

   {Steam coil}, a coil of pipe, or collection of connected
      pipes, for containing steam; -- used for heating, drying,
      etc.

   {Steam colors} (Calico Printing), colors in which the
      chemical reaction fixed the coloring matter in the fiber
      is produced by steam.

   {Steam cylinder}, the cylinder of a steam engine, which
      contains the piston. See Illust. of {Slide valve}, under
      {Slide}.

   {Steam dome} (Steam Boilers), a chamber upon the top of the
      boiler, from which steam is conduced to the engine. See
      Illust. of Steam boiler, above.

   {Steam fire engine}, a fire engine consisting of a steam
      boiler and engine, and pump which is driven by the engine,
      combined and mounted on wheels. It is usually drawn by
      horses, but is sometimes made self-propelling.

   {Steam fitter}, a fitter of steam pipes.

   {Steam fitting}, the act or the occupation of a steam fitter;
      also, a pipe fitting for steam pipes.

   {Steam gas}. See {Superheated steam}, above.

   {Steam gauge}, an instrument for indicating the pressure of
      the steam in a boiler. The {mercurial steam gauge} is a
      bent tube partially filled with mercury, one end of which
      is connected with the boiler while the other is open to
      the air, so that the steam by its pressure raises the
      mercury in the long limb of the tume to a height
      proportioned to that pressure. A more common form,
      especially for high pressures, consists of a spring
      pressed upon by the steam, and connected with the pointer
      of a dial. The spring may be a flattened, bent tube,
      closed at one end, which the entering steam tends to
      straighten, or it may be a diaphragm of elastic metal, or
      a mass of confined air, etc.

   {Steam gun}, a machine or contrivance from which projectiles
      may be thrown by the elastic force of steam.

   {Steam hammer}, a hammer for forging, which is worked
      directly by steam; especially, a hammer which is guided
      vertically and operated by a vertical steam cylinder
      located directly over an anvil. In the variety known as
      Nasmyth's, the cylinder is fixed, and the hammer is
      attached to the piston rod. In that known as Condie's, the
      piston is fixed, and the hammer attached to the lower end
      of the cylinder.

   {Steam heater}.
      (a) A radiator heated by steam.
      (b) An apparatus consisting of a steam boiler, radiator,
          piping, and fixures for warming a house by steam.

   {Steam jacket}. See under {Jacket}.

   {Steam packet}, a packet or vessel propelled by steam, and
      running periodically between certain ports.

   {Steam pipe}, any pipe for conveying steam; specifically, a
      pipe through which steam is supplied to an engine.

   {Steam plow} or {plough}, a plow, or gang of plows, moved by
      a steam engine.

   {Steam port}, an opening for steam to pass through, as from
      the steam chest into the cylinder.

   {Steam power}, the force or energy of steam applied to
      produce results; power derived from a steam engine.

   {Steam propeller}. See {Propeller}.

   {Steam pump}, a small pumping engine operated by steam. It is
      usually direct-acting.

   {Steam room} (Steam Boilers), the space in the boiler above
      the water level, and in the dome, which contains steam.

   {Steam table}, a table on which are dishes heated by steam
      for keeping food warm in the carving room of a hotel,
      restaurant, etc.

   {Steam trap}, a self-acting device by means of which water
      that accumulates in a pipe or vessel containing steam will
      be discharged without permitting steam to escape.

   {Steam tug}, a steam vessel used in towing or propelling
      ships.

   {Steam vessel}, a vessel propelled by steam; a steamboat or
      steamship; -- a steamer.

   {Steam whistle}, an apparatus attached to a steam boiler, as
      of a locomotive, through which steam is rapidly
      discharged, producing a loud whistle which serves as a
      warning signal. The steam issues from a narrow annular
      orifice around the upper edge of the lower cup or
      hemisphere, striking the thin edge of the bell above it,
      and producing sound in the manner of an organ pipe or a
      common whistle.

Source : WordNet®

steam whistle
     n : a whistle in which the sound is produced by steam; usually
         attached to a steam boiler