palladium

from The Century Dictionary.

• noun A statue or image of the goddess Pallas; especially, in art and legend, a xoanon image. On the preservation of such an image, according to the legend, depended the safety of Troy.
• noun 2. Anything believed or reputed to afford effectual defense, protection, and safety: as, trial by jury is the palladium of our civil rights.
• noun Chemical symbol, Pd; atomic weight, 106.5. One of the rare metals associated with platinum.

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

• noun (Gr. Antiq.) Any statue of the goddess Pallas; esp., the famous statue on the preservation of which depended the safety of ancient Troy.
• noun That which affords effectual protection or security; a safeguard.
• noun (Chem.) A rare metallic element of the light platinum group, found native, and also alloyed with platinum and gold. It is a silver-white metal resembling platinum, and like it permanent and untarnished in the air, but is more easily fusible, with a melting point of 1555° C. It can also be prepared as a finely divided black powder. It is unique in its power of absorbing hydrogen, which it does to the extent of nearly a thousand volumes, forming the alloy Pd2H. It is used for graduated circles and verniers, for plating certain silver goods, and somewhat in dentistry. It was so named in 1804 by Wollaston from the asteroid Pallas, which was discovered in 1802. Symbol Pd. Atomic number, 46. Atomic weight, 106.42. Density 12.0.

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

• noun A safeguard (from a statue of Athena that was believed to safeguard the ancient city of Troy).
• noun A metallic chemical element (symbol Pd) with an atomic number of 46.

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

• noun a silver-white metallic element of the platinum group that resembles platinum; occurs in some copper and nickel ores; does not tarnish at ordinary temperatures and is used (alloyed with gold) in jewelry