The Collaborative International Dictionary of English v.0.48:

bootlicker \bootlicker\ n.
   someone who humbles himself as a sign of respect; who behaves
   as he had no self-respect.

   Syn: apple polisher, bootlick, fawner, groveller, truckler,
        ass-kisser, toady.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bootlicker
    n 1: someone who humbles himself as a sign of respect; who
         behaves as if he had no self-respect [syn: apple
         polisher, bootlicker, fawner, groveller, groveler,
         truckler]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "bootlicker":
   apple-polisher, ass-licker, backscratcher, backslapper, bootlick,
   brown-nose, brownie, clawback, courtier, creature, cringer, dupe,
   fawner, flatterer, flunky, footlicker, groveler, handshaker, helot,
   instrument, jackal, kowtower, lackey, led captain, lickspit,
   lickspittle, mealymouth, minion, peon, puppet, serf, slave,
   spaniel, stooge, suck, sycophant, timeserver, toad, toadeater,
   toady, tool, truckler, tufthunter, yes-man