definition of
OS

[1] #1 OS n. [os] 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] (computer science) software that controls the execution of computer programs and may provide various services. wn

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

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