WordNet (r) 3.0 (2006):

tightrope walker
    n 1: an acrobat who performs on a tightrope or slack rope [syn:
         funambulist, tightrope walker]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "tightrope walker":
   acrobat, aerialist, bareback rider, circus artist, clown,
   contortionist, equestrian director, equilibrist, flier,
   funambulist, gymnast, high wire artist, high-wire artist, juggler,
   lion tamer, palaestrian, pancratiast, ringmaster, ropewalker,
   slack-rope artist, snake charmer, sword swallower, trapeze artist,
   tumbler, weightlifter