What is the meaning of os?

noun

• 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