The Collaborative International Dictionary of English v.0.48:

Columbium \Co*lum"bi*um\, n. [NL., fr. Columbia America.]
   (Chem.)
   A rare element of the vanadium group, first found in a
   variety of the mineral columbite occurring in Connecticut,
   probably at Haddam. Atomic weight 94.2. Symbol Cb or Nb. Now
   more commonly called niobium.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

niobium \ni*o"bi*um\, n. [NL., fr. L. & E. Niobe.] (Chem.)
   The chemical element of atomic number 41. Chemical symbol Nb.
   Atomic weight 92.91. Previously called columbium. See also
   Columbium.
   [1913 Webster]

WordNet (r) 3.0 (2006):

niobium
    n 1: a soft grey ductile metallic element used in alloys; occurs
         in niobite; formerly called columbium [syn: niobium,
         Nb, atomic number 41]