The Collaborative International Dictionary of English v.0.48:

Topple \Top"ple\, v. i. [imp. & p. p. Toppled; p. pr. & vb. n.
   Toppling.] [From Top summit.]
   To fall forward; to pitch or tumble down.
   [1913 Webster]

         Though castles topple on their warders' heads. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Topple \Top"ple\, v. t.
   To throw down; to overturn.
   [1913 Webster]

         He topple crags from the precipice.      --Longfellow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

topple
    v 1: fall down, as if collapsing; "The tower of the World Trade
         Center tumbled after the plane hit it" [syn: tumble,
         topple]
    2: cause to topple or tumble by pushing [syn: topple,
       tumble, tip]

Moby Thesaurus II by Grady Ward, 1.0:

115 Moby Thesaurus words for "topple":
   ataxia, bite the dust, blow down, blow over, bowl down, bowl over,
   break down, break up, bring down, bulldog, capsize, careen,
   cast down, cave in, chaos, chop down, clutter, collapse,
   come a cropper, crumble, crumble to dust, culbuter, cut down,
   dash down, deck, defeat, disarray, disintegrate, disorder, down,
   drop, fall, fall down, fall flat, fall headlong, fall in,
   fall over, fall prostrate, fall to pieces, falter, fell,
   fetch down, floor, flounder, founder, get a cropper, go down,
   go to pieces, ground, hew down, huddle, keel over, knock down,
   knock over, lay level, lay low, lay out, level, list, lurch,
   mow down, muddle, oust, overcome, overset, overthrow, overturn,
   pitch, plunge, precipitate, prostrate, pull down, rase, raze,
   send headlong, slump, snarl, sprawl, spread-eagle, stagger,
   stammer, stumble, subvert, supinate, sway, take a fall,
   take a flop, take a header, take a pratfall, take a spill,
   take down, throw, throw down, tilt, tip over, topple down,
   topple over, topsy-turvify, topsy-turviness, topsy-turvy, totter,
   trip, tumble, turn a somersault, turn over, turn topsy-turvy,
   turn turtle, turn upside down, unhorse, unseat, upset, upturn,
   vanquish, whack down, wobble