Source : Webster's Revised Unabridged Dictionary (1913)

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}.

Source : WordNet®

columbium
     n : a former name for niobium