WordNet (r) 3.0 (2006):

overkill
    n 1: the capability to obliterate a target with more weapons
         (especially nuclear weapons) than are required
    2: any effort that seems to go farther than would be necessary
       to achieve its goal

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "overkill":
   aggrandizement, aggravated assault, aggression, amphibious attack,
   amplification, armed assault, assailing, assailment, assault,
   attack, ballyhoo, banzai attack, big talk, blitz, blitzkrieg,
   blowing up, breakthrough, burlesque, caricature, charge,
   counterattack, counteroffensive, coup de main, crippling attack,
   dead set at, descent on, dilatation, dilation, diversion,
   diversionary attack, drive, enhancement, enlargement, exaggerating,
   exaggeration, excess, exorbitance, expansion, extravagance,
   extreme, flank attack, frontal attack, gas attack, grandiloquence,
   head-on attack, heightening, huckstering, hyperbole, hyperbolism,
   infiltration, inflation, inordinacy, lightning attack,
   lightning war, magnification, mass attack, megadeath, mugging,
   offense, offensive, onset, onslaught, overabundance, overemphasis,
   overestimation, overflow, overmuch, overplus, overstatement,
   panzer warfare, plethora, prodigality, profuseness, puffery,
   puffing up, push, run against, run at, rush, sally, sensationalism,
   shock tactics, sortie, stretching, strike, superfluity,
   superlative, surfeit, surplus, surplusage, tall talk, touting,
   travesty, unprovoked assault