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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 symbol for osmium.
mountain massif, nomos (department) of Larissa, eastern Thessaly, Greece. It lies on the Gulf of Thermai and is separated on the north from the Olympus massif by the Vale of Tempe (Tembi). Rising from a broad, steep-sided plateau to a pyramidal peak of 6,489 feet (1,978 m), the mountain is noted in mythology for the attempt of the Aloads, sons of the sea god Poseidon, to climb to heaven by placing Ossa on Olympus and the Pelion mountains on Ossa.
(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.