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)

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "emission":
   blowout, discharge, disgorgement, effusion, egestion, ejaculation,
   ejection, elimination, emanation, emergence, emersion, eructation,
   eruption, excretion, expulsion, extravasation, extrusion,
   exudation, flow, flux, issuance, issue, jet, outburst, outpour,
   secretion, spout, spurt, squirt, surfacing, transudation, vent



Bouvier's Law Dictionary, Revised 6th Ed (1856):

EMISSION, med. jur. The act by which any matter whatever is thrown from the
body; thus it is usual to say, emission of urine, emission of semen, &c.
     2. In cases of rape, when the fact of penetration is proved, it may be
left to the jury whether emission did or did not take place. Proof of
emission would perhaps be held to be evidence of penetration. Addis. R. 143;
2 So. Car. Const. R. 351; 2 Chitty, Crim. Law, 810; 1 Beck's Med. Jur. 140 1
Russ. C. & M. 560; 1 East, P. C. 437.