The Collaborative International Dictionary of English v.0.48:

Quash \Quash\, v. i.
   To be shaken, or dashed about, with noise.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quash \Quash\, n.
   Same as Squash.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quash \Quash\, v. t. [imp. & p. p. Quashed; p. pr. & vb. n.
   Quashing.] [OF. quasser, F. casser, fr. L. cassare to
   annihilate, annul, fr. cassus empty, vain, of uncertain
   origin. The word has been confused with L. quassare to shake,
   F. casser to break, which is probably of different origin.
   Cf. Cashier, v. t.] (Law)
   To abate, annul, overthrow, or make void; as, to quash an
   indictment. --Blackstone.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quash \Quash\, v. t. [OF. quasser, F. casser, fr. L. quassare to
   shake, shatter, shiver, v. intens. fr. quatere, quassum, to
   shake, shatter. Cf. Concussion, Discuss, Rescue, and
   also Quash to annul.]
   1. To beat down, or beat in pieces; to dash forcibly; to
      crush.
      [1913 Webster]

            The whales
            Against sharp rocks, like reeling vessels, quashed,
            Though huge as mountains, are in pieces dashed.
                                                  --Waller.
      [1913 Webster]

   2. To crush; to subdue; to suppress or extinguish summarily
      and completely; as, to quash a rebellion.
      [1913 Webster]

            Contrition is apt to quash or allay all worldly
            grief.                                --Barrow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

quash
    v 1: put down by force or intimidation; "The government quashes
         any attempt of an uprising"; "China keeps down her
         dissidents very efficiently"; "The rich landowners
         subjugated the peasants working the land" [syn: repress,
         quash, keep down, subdue, subjugate, reduce]
    2: declare invalid; "The contract was annulled"; "void a plea"
       [syn: invalidate, annul, quash, void, avoid,
       nullify] [ant: formalise, formalize, validate]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "quash":
   abate, abrogate, annihilate, annul, asphyxiate, black out,
   bottle up, cancel, censor, choke, choke off, clamp down on, cork,
   cork up, crack down on, crush, damp down, discharge, dissolve,
   drown, extinguish, gag, hold down, hugger-mugger, hush, hush up,
   hush-hush, invalidate, jump on, keep down, keep under, kill,
   muffle, muzzle, negate, nullify, overrule, overthrow, overwhelm,
   pour water on, put down, put out, quell, quench, reject, repress,
   rescind, reverse, revoke, set aside, shush, shut down on, silence,
   sit down on, sit on, smash, smother, snuff out, squash, squelch,
   stamp out, stanch, stifle, strangle, stultify, subdue, suffocate,
   suppress, throttle, throw out, trample out, trample underfoot,
   undo, vacate, vitiate, void