1. A mouth or mouthlike opening
   "The cervical os dilates during childbirth"

1. Rigid connective tissue that makes up the skeleton of vertebrates
   "The os[2] of the skull protects the brain";
   - bone

1. The left eye
   "The patient complained of blurred vision in the OS";
   - oculus sinister
    
2. (computing) software that controls the execution of computer programs and may provide various services
   "Windows and macOS are popular OSs for personal computers";
   - operating system

1. A hard brittle blue-grey or blue-black metallic element that is one of the platinum metals; the heaviest metal known
   - osmium, atomic number 76

1. The 15th letter of the Roman alphabet
   "He drew a perfect O in the sand";
   - O

Derived forms: ossa, ora

Type of: alphabetic character, computer software, connective tissue, eye, letter, letter of the alphabet, metal, metallic element, oculus [rare], opening, optic, orifice, package, porta, software, software package, software program, software system

Part of: endoskeleton, horn, Latin alphabet, platform, Roman alphabet

Encyclopedia: Os, Ton van