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):

injection
    n 1: the forceful insertion of a substance under pressure
    2: any solution that is injected (as into the skin) [syn:
       injection, injectant]
    3: the act of putting a liquid into the body by means of a
       syringe; "the nurse gave him a flu shot" [syn: injection,
       shot]

Moby Thesaurus II by Grady Ward, 1.0:

137 Moby Thesaurus words for "injection":
   Earth insertion, LEM, LM, antitoxin, apogee, aside,
   attitude-control rocket, bag, ballistic capsule, bang, booster,
   booster dose, booster shot, brewing, burn, capsule, deck,
   deep-space ship, docking, docking maneuver, dose, draft, drench,
   drenching, dropping, drug packet, ducking, dunking, embedment,
   encroachment, entrance, entrenchment, episode, ferry rocket, fix,
   fuel ship, graft, grafting, hit, hypodermic, hypodermic injection,
   imbruement, imbuement, impaction, impactment, impingement,
   implantation, imposition, impregnation, incursion, infiltration,
   infix, infixion, influx, infringement, infusion, inoculation,
   inroad, insert, insertion, insinuation, intercalation,
   interference, interjection, interlineation, interlocution,
   interloping, interpolation, interposition, interposure,
   interruption, intervention, introduction, intromission, intrusion,
   invasion, irruption, jet injection, leaching, lixiviation,
   lunar excursion module, lunar module, maceration, mainlining,
   manned rocket, module, moon ship, multistage rocket,
   narcotic injection, narcotic shot, obiter dictum, obtrusion, orbit,
   overdose, parenthesis, parking orbit, penetration, percolation,
   perfusion, perigee, permeation, popping, portion, potion, pulping,
   reentry, remark, rocket, saturation, seething, shooting up, shot,
   shuttle rocket, side remark, skin-popping, soak, soakage, soaking,
   soft landing, sopping, souse, sousing, space capsule,
   space docking, space rocket, spacecraft, spaceship, steeping,
   tessellation, tossing-in, transplant, transplantation, trespass,
   trespassing, unlawful entry, vaccination, vaccine



The Free On-line Dictionary of Computing (30 December 2018):

injection

   1.  A function, f : A -> B, is injective or
   one-one, or is an injection, if and only if

   	for all a, b in A, f(a) = f(b) => a = b.

   I.e. no two different inputs give the same output (contrast
   many-to-one).  This is sometimes called an embedding.  Only
   injective functions have left inverses f' where f'(f(x)) = x,
   since if f were not an injection, there would be elements of B
   for which the value of f' was not unique.  If an injective
   function is also a surjection then is it a bijection.

   2.  An injection function is one which takes
   objects of type T and returns objects of type C(T) where C is
   some type constructor.  An example is

   	f x = (x, 0).

   The opposite of an injection function is a projection
   function which extracts a component of a constructed object,
   e.g.

   	fst (x,y) = x.

   We say that f injects its argument into the data type and fst
   projects it out.

   (1995-03-14)