os

(noun) a mouth or mouthlike opening.

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

(noun) (computer science) software that controls the execution of computer programs and may provide various services. Synonyms: operating system, OS.

(noun) the left eye. Synonyms: oculus sinister, OS.

(noun) rigid connective tissue that makes up the skeleton of vertebrates. Synonyms: bone.