Nb vs columbium

Nb and columbium both are nouns.

Word	Noun	Adjective	Verb	Adverb
Nb	Yes	No	No	No
columbium	Yes	No	No	No

As nouns, columbium is a hyponym of Nb; that is, columbium is a word with a more specific, narrower meaning than Nb:

Nb: a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium
columbium: a former name for niobium

Nb (noun)	columbium (noun)
a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium	a former name for niobium