Noun has 2 senses

• nb(n = noun.substance) atomic number 41, niobium - a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium;




• 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"