Vitamin A

vitamin A   n.  A fat-soluble vitamin or a mixture of vitamins, especially vitamin A1 or a mixture of vitamins A1 and A2, occurring principally in fish-liver oils, milk, and some yellow and dark green vegetables, and functioning in normal cell growth and development. Its deficiency causes hardening and roughening of the skin, night blindness, and degeneration of mucous membranes. Also called retinol.

Main Entry: vitamin A
Function: noun
: any of several fat-soluble vitamins or a mixture of two or more of them whose lack in the animal body causes keratinization ofepithelial tissues (as in the eye with resulting night blindness and xerophthalmia): as a : a pale yellow crystalline highly unsaturated alicyclic alcoholC₂₀H₂₉OH that is found in animal products (as egg yolk, milk, and butter) and especially in marine fish-liver oils (as of cod, halibut, and shark) and that is used in variousforms in medicine and nutrition called also retinol, vitamin A₁ b : a yellow viscous liquid alicyclic alcohol C₂₀H₂₇OH that contains onemore double bond in a molecule than vitamin A₁ and is less active biologically in mammals and that occurs especially in the liver oil of freshwater fish called also vitaminA₂

vitamin A n.
A fat-soluble vitamin or a mixture of vitamins, especially vitamin A₁ or a mixture of vitamins A₁ and A₂, occurring principally in fish-liver oils, milk, and some yellow and dark green vegetables, and functioning in normal cell growth and development with deficiencies causing hardening and roughening of the skin, night blindness, and degeneration of mucous membranes. Also called retinol.