WordNet (r) 3.0 (2006):

whomp
    v 1: hit with the hand [syn: cuff, whomp]
    2: beat overwhelmingly

Moby Thesaurus II by Grady Ward, 1.0:

110 Moby Thesaurus words for "whomp":
   appulse, bang, bang into, beat, blank, blow, box, box the ears,
   brunt, buffet, bulldoze, bulldozing, bulling, bump, bump into,
   burst, bust, cannon, carambole, carom, carom into, clap, clash,
   clobber, collide, collision, come into collision, concuss,
   concussion, confront each other, crack, crack up, crack-up, crash,
   crash into, cream, crump, crunch, cuff, dash into, defeat utterly,
   drub, encounter, fall foul of, flap, flop, foul, hammering, hit,
   hit against, hurt, hurtle, impact, impinge, impingement, knock,
   knock against, lambaste, mauling, meet, meeting, onslaught,
   overbear, overwhelm, paste, percuss, percussion, ramming, rap,
   report, run into, schmear, shellac, shock, shut out, sideswipe,
   skunk, slam, slam into, slap, slap the face, slat, sledgehammering,
   smack, smack into, smash, smash into, smash up, smash-up, smashing,
   smear, snow under, splat, steamroller, strike, strike against,
   swap, tap, thrash, thrusting, thwack, token punishment, trounce,
   wallop, whack, wham, whap, whelm, whitewash, whop