1.  nb(n = noun.substance) atomic number 41, niobium - a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium;
is a kind of metal, metallic element
has particulars: columbium

2.  nb(n = noun.communication) n.b., nota bene - a Latin phrase (or its abbreviation) used to indicate that special attention should be paid to something; "the margins of his book were generously supplied with pencilled NBs"
is a kind of annotation, notation, note

nb, abbr.
1 US Nebraska (in official postal use).
2 New Brunswick.
3 no ball.
4 Scotland (North Britain).
5 nota bene.

nb, symb. Chem. the element niobium.