thiamin vs vitamin B

thiamin and vitamin B both are nouns.

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

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

thiamin: a B vitamin that prevents beriberi; maintains appetite and growth
vitamin B: originally thought to be a single vitamin but now separated into several B vitamins

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

thiamin (noun)	vitamin B (noun)
a B vitamin that prevents beriberi; maintains appetite and growth	originally thought to be a single vitamin but now separated into several B vitamins