WordNet (r) 3.0 (2006):

hillbilly
    n 1: a disparaging term for an unsophisticated person [syn:
         hillbilly, bushwhacker]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "hillbilly":
   backwoodsman, boor, briar-hopper, brush ape, bucolic, bumpkin,
   bushman, clam digger, clod, clodhopper, clown, country bumpkin,
   cracker, desert rat, farmer, forester, frontiersman, hayseed, hick,
   hinterlander, looby, lout, mountain man, mountaineer, piny,
   redneck, ridge runner, rube, rustic, woodlander, woodman, woodsman,
   yokel