n. 1. a vitamin essential for normal vision (C20H30O); it prevents night blindness or inflammation or dryness of the eyes; same as vitamin A. One U.S.P. unit of vitamin A is equivalent to 0.30 micrograms of pure vitamin A alcohol. Syn. -- vitamin A; vitamin A alcohol; antiophthalmic factor; biosterol; retinol; A. [ WordNet 1.5 +PJC ]
(n) any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes, Syn.A, axerophthol, antiophthalmic factor