The Collaborative International Dictionary of English v.0.48:

Expulsion \Ex*pul"sion\, n. [L. expulsio, fr. expellere: cf. F.
   expulsion. See Expel.]
   1. The act of expelling; a driving or forcing out; summary
      removal from membership, association, etc.
      [1913 Webster]

            The expulsion of the Tarquins.        --Shak.
      [1913 Webster]

   2. The state of being expelled or driven out.
      [1913 Webster]

WordNet (r) 3.0 (2006):

expulsion
    n 1: 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]
    2: squeezing out by applying pressure; "an unexpected extrusion
       of toothpaste from the bottom of the tube"; "the expulsion of
       pus from the pimple" [syn: extrusion, expulsion]
    3: the act of expelling or projecting or ejecting [syn:
       expulsion, projection, ejection, forcing out]