The Collaborative International Dictionary of English v.0.48:

Injection \In*jec"tion\, n. [L. injectio : cf. F. injection.]
   1. The act of injecting or throwing in; -- applied
      particularly to the forcible insertion of a liquid or gas,
      by means of a syringe, pump, etc.
      [1913 Webster]

   2. That which is injected; especially, a liquid inserted
      thrown into a cavity of the body by a syringe or pipe; a
      clyster; an enema. --Mayne.
      [1913 Webster]

   3. (Anat.)
      (a) The act or process of filling vessels, cavities, or
          tissues with a fluid or other substance.
      (b) A specimen prepared by injection.
          [1913 Webster]

   4. (Steam Eng.)
      (a) The act of throwing cold water into a condenser to
          produce a vacuum.
      (b) The cold water thrown into a condenser.
          [1913 Webster]

   Injection cock, or Injection valve (Steam Eng.), the cock
      or valve through which cold water is admitted into a
      condenser.

   Injection condenser. See under Condenser.

   Injection pipe, the pipe through which cold water is
      through into the condenser of a steam engine.

   fuel injection, a method of inserting fuel into
      internal-combustion engines by directly forcing the liquid
      fuel into the combustion chamber at an appropriate point
      in the piston cycle; in contrast to carburetion, in
      which an air-fuel mixture is drawn in by the downward
      stroke of the piston.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

fuel injection
    n 1: mechanical system to inject atomized fuel directly into the
         cylinders of an internal-combustion engine; avoids the need
         for a carburetor [syn: fuel injection, fuel injection
         system]