definition of
os

[1] #1 os n. a mouth or mouthlike opening. wn

[2] #2 os n. [osmium, Os, atomic number 76] a hard brittle blue-grey or blue-black metallic element that is one of the platinum metals; the heaviest metal known. wn

[3] #3 os n. [operating system, OS] (computer science) software that controls the execution of computer programs and may provide various services. wn

[4] #4 os n. [oculus sinister, OS] the left eye. wn

[5] #5 os n. [bone] rigid connective tissue that makes up the skeleton of vertebrates. wn