WordNet (r) 3.0 (2006):

slithering
    adj 1: moving as on a slippery surface; "his slipping and
           slithering progress over the ice" [syn: slipping,
           slithering]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "slithering":
   amphibian, anguine, batrachian, coasting, colubriform, crawling,
   creeping, crocodilian, flow, flowing, froggy, glide, gliding,
   lizardlike, ophidian, repent, reptant, reptile, reptilelike,
   reptilian, reptiliform, reptiloid, sailing, saurian, serpentiform,
   serpentile, serpentine, serpentlike, serpentoid, skating, skiing,
   skim, sledding, slide, sliding, slipping, slither, snakelike,
   snaky, sweep, sweeping, toadish, tobogganing, viperiform, viperish,
   viperlike, viperoid, viperous, vipery