\Boil"er\, n.
1. One who boils.
2. A vessel in which any thing is boiled.
Note: The word boiler is a generic term covering a great
      variety of kettles, saucepans, clothes boilers,
      evaporators, coppers, retorts, etc.
3. (Mech.) A strong metallic vessel, usually of wrought iron
   plates riveted together, or a composite structure
   variously formed, in which steam is generated for driving
   engines, or for heating, cooking, or other purposes.
Note: The earliest steam boilers were usually spheres or
      sections of spheres, heated wholly from the outside.
      Watt used the wagon boiler (shaped like the top of a
      covered wagon) which is still used with low pressures.
      Most of the boilers in present use may be classified as
      plain cylinder boilers, flue boilers, sectional and
      tubular boilers.
{Barrel of a boiler}, the cylindrical part containing the
   flues.
{Boiler plate}, {Boiler iron}, plate or rolled iron of about
   a quarter to a half inch in thickness, used for making
   boilers and tanks, for covering ships, etc.
{Cylinder boiler}, one which consists of a single iron
   cylinder.
{Flue boilers} are usually single shells containing a small
   number of large flues, through which the heat either
   passes from the fire or returns to the chimney, and
   sometimes containing a fire box inclosed by water.
{Locomotive boiler}, a boiler which contains an inclosed fire
   box and a large number of small flues leading to the
   chimney.
{Multiflue boiler}. Same as {Tubular boiler}, below.
{Sectional boiler}, a boiler composed of a number of
   sections, which are usually of small capacity and similar
   to, and connected with, each other. By multiplication of
   the sections a boiler of any desired capacity can be built
   up.
{Tubular boiler}, a boiler containing tubes which form flues,
   and are surrounded by the water contained in the boiler.
   See Illust. {of Steam boiler}, under {Steam}.
{Tubulous boiler}. See under {Tubulous}. See {Tube}, n., 6,
   and 1st {Flue}.

\Boil"er\, n.
A sunken reef; esp., a coral reef on which the sea breaks
heavily.