B vitamin vs B-complex vitamin

B vitamin and B-complex vitamin both are nouns.

Word	Noun	Adjective	Verb	Adverb
B vitamin	Yes	No	No	No
B-complex vitamin	Yes	No	No	No

As nouns, B vitamin and B-complex vitamin are synonyms defined as:

B vitamin and B-complex vitamin: originally thought to be a single vitamin but now separated into several B vitamins

Other synonyms of B vitamin include B, B complex, vitamin B, vitamin B complex.

B vitamin (noun)	B-complex vitamin (noun)
originally thought to be a single vitamin but now separated into several B vitamins	originally thought to be a single vitamin but now separated into several B vitamins