Source : Webster's Revised Unabridged Dictionary (1913)

Tantalum \Tan"ta*lum\, n. [NL. So named on account of the
   perplexity and difficulty encounterd by its discoverer
   (Ekeberg) in isolating it. See {Tantalus}.] (Chem.)
   A rare nonmetallic element found in certain minerals, as
   tantalite, samarskite, and fergusonite, and isolated as a
   dark powder which becomes steel-gray by burnishing. Symbol
   Ta. Atomic weight 182.0. Formerly called also {tantalium}.

Source : WordNet®

tantalum
     n : a hard gray lustrous metallic element that is highly
         corrosion-resistant; occurs in niobite and fergusonite
         and tantalite [syn: {Ta}, {atomic number 73}]