WordNet (r) 3.0 (2006):

water-skiing
    n 1: skiing on water while being towed by a motorboat

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "waterskiing":
   Australian crawl, aquaplaning, aquatics, backstroke, balneation,
   bathe, bathing, breaststroke, butterfly, crawl, diving, dog paddle,
   fin, fishtail, flapper, flipper, floating, natation, sidestroke,
   surfboarding, surfing, swim, swimming, treading water, wading