osmium(n = noun.substance) atomic number 76, os - a hard brittle blue-grey or blue-black metallic element that is one of the platinum metals; the heaviest metal known;

   A rare metallic element of the platinum group with atomic number 76. It is 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 190.2. Specific gravity 22.477. [1913 Webster]

osmium, n. Chem. a hard bluish-white transition element, the heaviest known metal, occurring naturally in association with platinum and used in certain alloys.

Usage:
Symb.: Os.

Etymology:
Gk osme smell (from the pungent smell of its tetroxide)