os > define

A nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust.
- synonyms: oxygen, O, atomic number 8
The 15th letter of the Roman alphabet.
- synonyms: O, o
The blood group whose red cells carry neither the A nor B antigens.
- usage: "people with type O blood are universal donors"
- synonyms: O, type O, group O
A mouth or mouthlike opening.
A hard brittle blue-grey or blue-black metallic element that is one of the platinum metals; the heaviest metal known.
- synonyms: osmium, atomic number 76
Computer science. ( software that controls the execution of computer programs and may provide various services)
- synonyms: operating system
The left eye.
- synonyms: oculus sinister
Rigid connective tissue that makes up the skeleton of vertebrates.
- synonyms: bone

(n.) A mouth; an opening; an entrance.
(n.) One of the ridges of sand or gravel found in Sweden, etc., supposed by some to be of marine origin, but probably formed by subglacial waters. The osar are similar to the kames of Scotland and the eschars of Ireland. See Eschar.
(n.) A bone.

by Webster's Revised Unabridged Dictionary

(latin) OS - left eye

by Department of Defense Dictionary of Military and Associated Terms. 31 January 2011.