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From The Collaborative International Dictionary of English v.0.48:
osmium \os"mi*um\ ([o^]z"m[i^]*[u^]m), n. [Gr. 'osmh` a smell, odor, akin to 'o`zein 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 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 +PJC]