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blood type, 1926, originally "zero," denoting absence of A and B agglutinogens.
os 1 (ŏs)
n. pl. o·ra (ôr'ə)
An opening into a hollow organ or canal.
The oral cavity; mouth.
os 2 (ŏs)
n. pl. os·sa (ŏs'ə)
The symbol for the element osmium.
Latin oculus sinister (left eye)
The Greek letter omicron. Entries beginning with this character are alphabetized under omicron.
The symbol for the element oxygen.
The symbol for osmium.
The symbol for oxygen.
A hard, brittle, bluish-white metallic element that is the densest naturally occurring element. It is used to make very hard alloys for fountain pen points, electrical contacts, and instrument pivots. Atomic number 76; atomic weight 190.2; melting point 3,000°C; boiling point 5,000°C; specific gravity 22.57; valence 2, 3, 4, 8. See Periodic Table.
(Os), chemical element, one of the platinum metals of Group VIIIb of the periodic table and the densest naturally occurring element. A gray-white metal, osmium is very hard, brittle, and difficult to work, even at high temperatures. Of the platinum metals it has the highest melting point, so fusing and casting are difficult. Osmium wires were used for filaments of early incandescent lamps before the introduction of tungsten. It has been used chiefly as a hardener in alloys of the platinum metals, though ruthenium has generally replaced it. A hard alloy of osmium and iridium has been used for tips of fountain pens and phonograph needles, and osmium tetroxide is used in certain organic syntheses.