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]

Moby Thesaurus II by Grady Ward, 1.0:

228 Moby Thesaurus words for "suppression":
   Eighteenth Amendment, Prohibition Party, Volstead Act, abolishment,
   abolition, aloofness, annihilation, annulment, arrest, arrestation,
   arrestment, backwardness, bamboo curtain, ban, barrier of secrecy,
   bashfulness, blackout, blankness, block, blockage, blocking,
   bottling up, breaking, ceasing, censoring, censorship, cessation,
   check, checking, chilliness, choking, choking off, clogging,
   closing up, closure, coldness, concealing, concealment, conquering,
   constraint, constriction, contraband, control, controlling,
   conversion, coolness, corking up, crackdown, cramp, crushing,
   curtain, defense mechanism, delay, denial, deracination,
   detachment, detainment, detention, disallowance, discontinuation,
   discreetness, discretion, distance, domestication, elimination,
   embargo, end, ending, eradication, exclusion, expressionlessness,
   extermination, extinction, extinguishment, extirpation, fixation,
   foot-dragging, forbiddance, forbidden fruit, forbidding, frigidity,
   frostiness, gentling, guardedness, halt, halting, hampering,
   hiding, hindering, hindrance, holdback, holding, holding in,
   holdup, humbling, humiliation, hush-up, iciness, impassiveness,
   impassivity, impediment, impersonality, inaccessibility, index,
   index expurgatorius, index librorum prohibitorum, inhibition,
   injunction, interdict, interdicting, interdiction, interdictum,
   interference, interruption, introversion, iron curtain,
   ironbound security, keeping, law, let, liquidation, locking in,
   maintenance, mental block, modesty, negation, negativism, no-no,
   nuisance value, nullification, oath of secrecy, obstructing,
   obstruction, obstructionism, occlusion, official secrecy,
   opposition, pall, precluding, preclusion, prehension, preservation,
   prevention, prohibiting, prohibition, prohibitory injunction,
   proscription, psychological block, purge, put-down, putting down,
   quashing, quelling, quenching, quieting, reduction, refusal,
   rejection, remoteness, repression, reserve, reservedness,
   resistance, restraining, restraint, restriction,
   restrictive covenants, retainment, retardation, retardment,
   retention, retentiveness, retentivity, reticence, reticency,
   retirement, rooting out, ruling out, seal of secrecy, security,
   setback, silencing, smashing, smothering, snuffing out, squashing,
   squeeze, squelching, standoffishness, statute, stifling, stop,
   stopping, stranglehold, strangling, strangulation, stricture,
   subdual, subduedness, subduing, sublimation, suffocating,
   suffocation, sumptuary laws, surcease, symbolization, taboo,
   taming, tenacity, terminating, termination, throttling,
   treading down, unaffability, unapproachability, uncongeniality,
   undemonstrativeness, unexpansiveness, uprooting, veil,
   veil of secrecy, voiding, withdrawal, withdrawnness, withholding,
   wraps, zoning, zoning laws