Source : Webster's Revised Unabridged Dictionary (1913)

Osmium \Os"mi*um\, n. [Gr. ? a smell, odor, akin to ? to smell.
   So named in allusion to the strong chlorinelike odor of osmic
   tetroxide. See {Odor}.] (Chem.)
   A rare metallic element of the platinum group, found native
   as an alloy in platinum ore, and in iridosmine. It is a hard,
   infusible, bluish or grayish white metal, and the heaviest
   substance known. Its tetroxide is used in histological
   experiments to stain tissues. Symbol {Os}. Atomic weight
   191.1. Specific gravity 22.477.

Source : WordNet®

osmium
     n : a hard brittle blue-gray or blue-black metallic element that
         is one of the platinum metals; the heaviest metal known
         [syn: {Os}, {atomic number 76}]