vitamin A

noun
  1. a yellow, fat-soluble, solid terpene alcohol, C20H30O, obtained from carotene and occurring in green and yellow vegetables, egg yolk, etc.: essential to growth, the protection of epithelial tissue, and the prevention of night blindness.

Origin of vitamin A

First recorded in 1920–25
Also called vitamin A1, retinol.

vitamin A2

noun
  1. a yellow oil, C20H28O, similar to vitamin A, obtained from fish liver.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for vitamin a

vitamin A

noun
  1. a fat-soluble yellow unsaturated alcohol occurring in green and yellow vegetables (esp carrots), butter, egg yolk, and fish-liver oil (esp halibut oil). It is essential for the prevention of night blindness and the protection of epithelial tissue. Formula: C 20 H 30 OAlso called: vitamin A 1, retinol

vitamin A2

noun
  1. a vitamin that occurs in the tissues of freshwater fish and has a function similar to that of vitamin A. Formula: C 20 H 28 OAlso called: dehydroretinol
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

vitamin a in Medicine

vitamin A

n.
  1. 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.retinol

vitamin A2

n.
  1. A golden yellow oil occurring chiefly in the livers of freshwater fish and having about 40 percent of the biological activity of vitamin A1.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

vitamin a in Science

vitamin A

  1. A fat-soluble vitamin important for normal vision, tissue growth, and healthy skin. It is found in fish-liver oils, milk, green leafy vegetables, and red, orange, and yellow vegetables and fruits. A deficiency of vitamin A in humans causes poor vision at night and damage to the skin and mucous membranes. Also called retinol. Chemical formula: C20H30O.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.