Definitions for water ski
Random House Webster's College Dictionary
a ski on which to water-ski, designed to plane over water: it is shorter and broader than the ski used on snow.
Origin of water ski:
to plane over water on water skis by grasping a towing rope pulled by a speedboat.
broad ski for skimming over water towed by a speedboat
ride water skis
A broad ski used for water skiing
To ride on water skis