Source : Webster's Revised Unabridged Dictionary (1913)

Niobium \Ni*o"bi*um\, n. [NL., fr. L. & E. {Niobe}.] (Chem.)
   A later name of columbium. See {Columbium}.

Source : WordNet®

niobium
     n : a soft gray ductile metallic element used in alloys; occurs
         in niobite; formerly called columbium [syn: {Nb}, {atomic
         number 41}]