The Collaborative International Dictionary of English v.0.48:

Suppression \Sup*pres"sion\, n. [L. suppressio: cf. F.
   suppression.]
   1. The act of suppressing, or the state of being suppressed;
      repression; as, the suppression of a riot, insurrection,
      or tumult; the suppression of truth, of reports, of
      evidence, and the like.
      [1913 Webster]

   2. (Med.) Complete stoppage of a natural secretion or
      excretion; as, suppression of urine; -- used in
      contradiction to retention, which signifies that the
      secretion or excretion is retained without expulsion.
      --Quain.
      [1913 Webster]

   3. (Gram.) Omission; as, the suppression of a word.
      [1913 Webster]

   Syn: Overthrow; destruction; concealment; repression;
        detention; retention; obstruction.
        [1913 Webster]

WordNet (r) 3.0 (2006):

suppression
    n 1: the failure to develop some part or organ
    2: the act of withholding or withdrawing some book or writing
       from publication or circulation; "a suppression of the
       newspaper" [syn: suppression, curtailment]
    3: forceful prevention; putting down by power or authority; "the
       suppression of heresy"; "the quelling of the rebellion"; "the
       stifling of all dissent" [syn: suppression, crushing,
       quelling, stifling]
    4: (psychology) the conscious exclusion of unacceptable thoughts
       or desires [syn: inhibition, suppression]