The Collaborative International Dictionary of English v.0.48:

Emission \E*mis"sion\, n. [L. emissio: cf. F. ['e]mission. See
   Emit.]
   1. The act of sending or throwing out; the act of sending
      forth or putting into circulation; issue; as, the emission
      of light from the sun; the emission of heat from a fire;
      the emission of bank notes.
      [1913 Webster]

   2. That which is sent out, issued, or put in circulation at
      one time; issue; as, the emission was mostly blood.
      [1913 Webster]

   Emission theory (Physics), the theory of Newton, regarding
      light as consisting of emitted particles or corpuscles.
      See Corpuscular theory, under Corpuscular.
      [1913 Webster]

WordNet (r) 3.0 (2006):

emission
    n 1: the act of emitting; causing to flow forth [syn:
         emission, emanation]
    2: a substance that is emitted or released [syn: discharge,
       emission]
    3: the release of electrons from parent atoms
    4: any of several bodily processes by which substances go out of
       the body; "the discharge of pus" [syn: discharge,
       emission, expelling]
    5: the occurrence of a flow of water (as from a pipe)