b vs B

b and B both are nouns.

Word	Noun	Adjective	Verb	Adverb
b	Yes	No	No	No
B	Yes	No	No	No

As nouns, b and B are synonyms defined as:

b (noun)	B (noun)
the 2nd letter of the Roman alphabet	aerobic rod-shaped spore-producing bacterium; often occurring in chainlike formations; found primarily in soil
(physics) a unit of nuclear cross section; the effective circular area that one particle presents to another as a target for an encounter	the blood group whose red cells carry the B antigen
	the 2nd letter of the Roman alphabet
	a logarithmic unit of sound intensity equal to 10 decibels
	a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder
	originally thought to be a single vitamin but now separated into several B vitamins