The Collaborative International Dictionary of English v.0.48:

ostracism \os"tra*cism\, n. [Gr. 'ostrakismo`s, fr.
   'ostraki`zein to ostracize. See Ostracize.]
   1. (Gr. Antiq.) Banishment by popular vote, -- a means
      adopted at Athens to rid the city of a person whose talent
      and influence gave umbrage.
      [1913 Webster]

   2. Banishment; exclusion; as, social ostracism.
      [1913 Webster]

            Public envy is as an ostracism, that eclipseth men
            when they grow too great.             --Bacon.
      [1913 Webster]

            Sentenced to a perpetual ostracism from the . . .
            confidence, and honors, and emoluments of his
            country.                              --A. Hamilton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ostracism
    n 1: the state of being banished or ostracized (excluded from
         society by general consent); "the association should get
         rid of its elderly members--not by euthanasia, of course,
         but by Coventry" [syn: banishment, ostracism,
         Coventry]
    2: the act of excluding someone from society by general consent