platinum

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A silver-white metallic element occurring in alluvial deposits in sperrylite and nickel ores, usually mixed with other metals such as iridium, osmium, or nickel. It is ductile and malleable, does not oxidize in air, and is used as a catalyst and in electrical components, jewelry, dentistry, and electroplating. Atomic number 78; atomic weight 195.08; melting point 1,768.2°C; boiling point 3,825°C; specific gravity 21.45 (20°C); valence 2, 3, 4. cross-reference: Periodic Table.
• noun A medium to light gray.

from The Century Dictionary.

• noun Chemical symbol, Pt; atomic weight, 194.9. An important metal, introduced into Europe about the middle of the eighteenth century from South America.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A metallic element of atomic number 78, one of the noble metals, classed with silver and gold as a precious metal, occurring native or alloyed with other metals and also as the platinum arsenide (sperrylite). It is a heavy tin-white metal which is ductile and malleable, but very infusible (melting point 1772° C), and characterized by its resistance to strong chemical reagents. It is used for crucibles in laboratory operations, as a catalyst, in jewelry, 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 195.1. Symbol Pt. Formerly called platina.
• noun (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.
• noun (Elec.) a kind of incandescent lamp of which the luminous medium is platinum. See under Incandescent.
• noun (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.
• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Of a whitish grey colour, like that of the metal.
• adjective Of a musical recording that has sold over one million copies (for singles), or two million (for albums).
• noun The metallic chemical element with atomic number 78 and symbol Pt.
• noun A whitish grey colour, like that of the metal.
• noun music A single or album that has achieved platinum sales, i.e. over 1 million or 2 million.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a heavy precious metallic element; grey-white and resistant to corroding; occurs in some nickel and copper ores and is also found native in some deposits