The Collaborative International Dictionary of English v.0.48:

Exclusion \Ex*clu"sion\, n. [L. exclusio: cf. F. exclusion. See
   Exclude.]
   1. The act of excluding, or of shutting out, whether by
      thrusting out or by preventing admission; a debarring;
      rejection; prohibition; the state of being excluded.
      [1913 Webster]

            His sad exclusion from the doors of bliss. --Milton.
      [1913 Webster]

            The exclusion of the duke from the crown of England
            and Ireland.                          --Hume.
      [1913 Webster]

   2. (Physiol.) The act of expelling or ejecting a fetus or an
      egg from the womb.
      [1913 Webster]

   3. Thing emitted. --Sir T. Browne.
      [1913 Webster]

WordNet (r) 3.0 (2006):

exclusion
    n 1: the state of being excluded [ant: inclusion]
    2: the state of being excommunicated [syn: excommunication,
       exclusion, censure]
    3: a deliberate act of omission; "with the exception of the
       children, everyone was told the news" [syn: exception,
       exclusion, elision]
    4: the act of forcing out someone or something; "the ejection of
       troublemakers by the police"; "the child's expulsion from
       school" [syn: ejection, exclusion, expulsion,
       riddance]