Source : Webster's Revised Unabridged Dictionary (1913)

Internal-combustion engine \Internal-combustion engine\) in
   which the heat or pressure energy necessary to produce motion
   is developed in the engine cylinder, as by the explosion of a
   gas, and not in a separate chamber, as in a steam-engine
   boiler. The gas used may be a fixed gas, or one derived from
   alcohol, ether, gasoline (petrol), naphtha, oil (petroleum),
   etc. There are three main classes: (1) {gas engines} proper,
   using fixed gases, as coal, blast-furnace, or producer gas;
   (2) engines using the vapor of a volatile fluid, as the
   typical {gasoline (petrol) engine}; (3) {oil engines}, using
   either an atomized spray or the vapor (produced by heat) of a
   comparatively heavy oil, as petroleum or kerosene. In all of
   these the gas is mixed with a definite amount of air, the
   charge is composed in the cylinder and is then exploded
   either by a flame of gas (

   {flame ignition} -- now little used), by a hot tube (

   {tube ignition}) or the like, by an electric spark (

   {electric ignition}, the usual method is gasoline engines, or
      by the heat of compression, as in the Diesel engine. Gas
      and oil engines are chiefly of the stationary type.
      Gasoline engines are largely used for automobile vehicles,
      boats, etc. Most internal-combustion engines use the Otto
      (four-stroke) cycle, though many use the two-stroke cycle.
      They are almost universally trunk engines and
      single-acting. Because of the intense heat produced by the
      frequent explosions, the cylinders must be cooled by a
      water jacket (

   {water-cooled}) or by air currents (

   {air cooled}) to give the maximum thermodynamic efficiency
      and to avoid excessive friction or seizing. Interne
\In*terne"\, n. [F.] (F. pron. [a^]N`t[^a]rn") (Med.)
   A resident physician in a hospital; a house physician.

Source : WordNet®

water-cooled
     adj : kept cool or designed to be kept cool by means of water
           especially circulating water; "a water-cooled engine"