vitamin A vs vitamin A2

vitamin A and vitamin A2 both are nouns.

Word	Noun	Adjective	Verb	Adverb
vitamin A	Yes	No	No	No
vitamin A2	Yes	No	No	No

As nouns, vitamin A2 is a hyponym of vitamin A; that is, vitamin A2 is a word with a more specific, narrower meaning than vitamin A:

vitamin A: any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes
vitamin A2: a viscous alcohol that is less active in mammals than is vitamin A1

Other hyponyms of vitamin A include retinol, vitamin A1, dehydroretinol.

vitamin A (noun)	vitamin A2 (noun)
any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes	a viscous alcohol that is less active in mammals than is vitamin A1