The Collaborative International Dictionary of English v.0.48:

Proscription \Pro*scrip"tion\, n. [L. proscriptio: cf. F.
   proscription.]
   1. The act of proscribing; a dooming to death or exile;
      outlawry; specifically, among the ancient Romans, the
      public offer of a reward for the head of a political
      enemy; as, under the triumvirate, many of the best Roman
      citizens fell by proscription.
      [1913 Webster]

            Every victory by either party had been followed by a
            sanguinary proscription.              --Macaulay.
      [1913 Webster]

   2. The state of being proscribed; denunciation; interdiction;
      prohibition. --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

proscription
    n 1: a decree that prohibits something [syn: prohibition,
         ban, proscription]
    2: rejection by means of an act of banishing or proscribing
       someone [syn: banishment, proscription]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "proscription":
   Eighteenth Amendment, Prohibition Party, Volstead Act, anathema,
   anathematizing, ban, banishment, blackball, blacklist, blasphemy,
   boundary, bounds, boycott, boycottage, censure, commination,
   condemnation, confinement, continence, contraband, conviction,
   curse, damnation, death sentence, death warrant, denial,
   denouncement, denunciation, disallowance, discipline, doom,
   embargo, evil eye, exclusion, excommunication, execration,
   forbiddance, forbidden fruit, forbidding, fulmination,
   guilty verdict, hex, imprecation, index, index expurgatorius,
   index librorum prohibitorum, inhibition, injunction, interdict,
   interdiction, interdictum, judgment, law, limit, limitation,
   malison, malocchio, moderation, no-no, ostracism, ostracization,
   preclusion, prescription, prevention, prohibition,
   prohibitory injunction, qualification, rap, refusal, rejection,
   repression, restrain, restriction, restrictive covenants,
   ruling out, sentence, statute, sumptuary laws, suppression, taboo,
   thundering, verdict of guilty, whammy, zoning, zoning laws