Source : Webster's Revised Unabridged Dictionary (1913)

Platinum \Plat"i*num\, n. [NL., fr. Sp. platina, from plata
   silver, LL. plata a thin plate of metal. See {Plate}, and cf.
   {Platina}.] (Chem.)
   A metallic element, intermediate in value between silver and
   gold, occurring native or alloyed with other metals, also as
   the platinum arsenide (sperrylite). It is heavy tin-white
   metal which is ductile and malleable, but very infusible, and
   characterized by its resistance to strong chemical reagents.
   It is used for crucibles, for stills for sulphuric acid,
   rarely for coin, and in the form of foil and wire for many
   purposes. Specific gravity 21.5. Atomic weight 194.3. Symbol
   Pt. Formerly called {platina}.

   {Platinum black} (Chem.), a soft, dull black powder,
      consisting of finely divided metallic platinum obtained by
      reduction and precipitation from its solutions. It absorbs
      oxygen to a high degree, and is employed as an oxidizer.
      

   {Platinum lamp} (Elec.), a kind of incandescent lamp of which
      the luminous medium is platinum. See under {Incandescent}.
      

   {Platinum metals} (Chem.), the group of metallic elements
      which in their chemical and physical properties resemble
      platinum. These consist of the light platinum group, viz.,
      rhodium, ruthenium, and palladium, whose specific
      gravities are about 12; and the heavy platinum group,
      viz., osmium, iridium, and platinum, whose specific
      gravities are over 21.

   {Platinum sponge} (Chem.), metallic platinum in a gray,
      porous, spongy form, obtained by reducing the double
      chloride of platinum and ammonium. It absorbs oxygen,
      hydrogen, and certain other gases, to a high degree, and
      is employed as an agent in oxidizing.

Source : WordNet®

platinum
     n : a heavy precious metallic element; gray-white and resistant
         to corroding; occurs in some nickel and copper ores and
         is also found native in some deposits [syn: {Pt}, {atomic
         number 78}]