The Collaborative International Dictionary of English v.0.48:

hitchhiker \hitchhiker\ n.
   a person who travels by getting free rides from passing
   vehicles; one who hitchhikes.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

hitchhiker
    n 1: a person who travels by getting free rides from passing
         vehicles

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "hitchhiker":
   ambulator, backpacker, foot passenger, foot soldier, foot traveler,
   footslogger, hiker, hoofer, infantryman, jaywalker, marcher,
   paddlefoot, pedestrian, peripatetic, trailsman, tramper, walker,
   walkist