The Collaborative International Dictionary of English v.0.48:

highchair \high"chair`\, high chair \high" chair`\n.
   a chair designed for feeding a very young child, having four
   long legs and a footrest and a detachable tray, which rests
   in front of the child, holds the food, and also serves as a
   restraint, to keep the child from falling out of the chair.

   Syn: feeding chair.
        [WordNet 1.5]