vitamin G vs B vitamin

vitamin G and B vitamin both are nouns.

Word	Noun	Adjective	Verb	Adverb
vitamin G	Yes	No	No	No
B vitamin	Yes	No	No	No

As nouns, B vitamin is a hypernym of vitamin G; that is, B vitamin is a word with a broader meaning than vitamin G:

vitamin G: a B vitamin that prevents skin lesions and weight loss
B vitamin: originally thought to be a single vitamin but now separated into several B vitamins

Other hypernyms of vitamin G include B-complex vitamin, B, B complex, vitamin B, vitamin B complex.

vitamin G (noun)	B vitamin (noun)
a B vitamin that prevents skin lesions and weight loss	originally thought to be a single vitamin but now separated into several B vitamins