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]

The Elements (07Nov00):

niobium
Symbol: Nb
Atomic number: 41
Atomic weight: 92.906
Soft, ductile grey-blue metallic transition element. Used in special
steels and in welded joints to increase strength. Combines with halogens
and oxidizes in air at 200 degrees celsius. Discovered by Charles
Hatchett
in 1801 and isolated by Blomstrand in 1864. Called columbium
originally.