1. (noun)vitamin A, antiophthalmic factor, axerophthol, A any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes Synonyms: antiophthalmic factor, adenine, axerophthol, vitamin A, group A, ampere, angstrom, angstromunit, deoxyadenosine monophosphate, amp, type A