vitamin a2(n = noun.substance) dehydroretinol - a viscous alcohol that is less active in mammals than is vitamin A1;
is a kind of a, antiophthalmic factor, axerophthol, vitamin a

   dehydroretinol (C20H28O), one of the substances also called vitamin A. It has about 40% of the bioactivity of vitamin A1. [WordNet 1.5]

b vitamin, b-complex vitamin, fat-soluble vitamin, vitamin, vitamin a, vitamin a1, vitamin b, vitamin b complex, vitamin b1, vitamin b12, vitamin b2, vitamin b3, vitamin b5, vitamin b6, vitamin bc, vitamin c, vitamin d, vitamin deficiency, vitamin e, vitamin g, vitamin h, vitamin k, vitamin k1, vitamin k2, vitamin k3, vitamin m, vitamin p, vitamin pill, water-soluble vitamin