- niobium, Nb, atomic number 41 - a soft gray ductile metallic element used in alloys; occurs in niobite; formerly called columbium
--1 is a kind of metallic element, metal
--1 is a substance of niobite, columbite
--1 has particulars: columbium - nota bene, NB, N.B. - 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"
--2 is a kind of note, annotation, notation