Synonyms for Nb (same or very similar meaning)
WordNet sense 1 (a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium):
niobiumWordNet sense 2 (a Latin phrase (or its abbreviation) used to indicate that special attention should be paid to something):
nota bene, N.B.From the ODE community, based on WordNetadd/edit