Any of several fat-soluble vitamins or a mixture of two or more of them whos lack in the animal body causes keratinization of epithelial tissues (as in the eye with resulting nyctalopia and xerophthalmia)
A pale yellow crystalline highly unsaturated alicyclic alcohol C20H29OH that occurs free or in the form of esters usu. along with smaller amounts of a cisisomer in animal products (as egg yolk, milk, and butter) and esp. in marine fish-liver oils (as of cod, halibut, and shark), that is systhesized biologically from carotene and other carotenoids and commercially, and that is used in various forms in medicine and nutrition (as in fortifying margarine and other foods and in supplementing animal feeds); all-trans-vitamin A.
A yellow viscous liquid alicyclic alcohol C20H27OH that contains one more double bond in the molecule than Vitamin A1 and is less active biologically in mammals and that occurs esp. in the liver oil of freshwater fish.
ref: Webster's International Unabridged Dictionary (all above)