Pronunciation: (oz'mē-um), [key]
a hard, heavy, metallic element having the greatest density of the known elements and forming octavalent compounds, as OsO4 and OsF8: used chiefly as a catalyst, in alloys, and in the manufacture of electric-light filaments. Symbol: Os; at. wt.: 190.2; at. no.: 76; sp. gr.: 22.57.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.