The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tantalum
    n 1: a hard grey lustrous metallic element that is highly
         resistant to corrosion; occurs in niobite and fergusonite
         and tantalite [syn: tantalum, Ta, atomic number 73]

The Elements (07Nov00):

tantalum
Symbol: Ta
Atomic number: 73
Atomic weight: 180.948
Heavy blue-grey metallic transition element. Ta-181 is a stable isotope,
and Ta-180 is a radioactive isotope, with a half-life in excess of 10^7
years. Used in surgery as it is unreactive. Forms a passive oxide layer
in
air. Identified in 1802 by Ekeberg and isolated in 1820 by Jons J.
Berzelius.