1. vitamin A2 - a viscous alcohol that is less active in mammals than is vitamin A1. dehydroretinol. antiophthalmic factor, axerophthol, vitamin A, A-any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes.. (Biochemistry) a vitamin that occurs in the tissues of freshwater fish and has a function similar to that of vitamin A. Formula: C20H28O.