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1. A mouth or mouthlike opening

1. Rigid connective tissue that makes up the skeleton of vertebrates
   - bone

1. The left eye
   - oculus sinister
    
2. (computer science) software that controls the execution of computer programs and may provide various services
   - 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
   - O

1. The blood group whose red cells carry neither the A nor B antigens
   "people with type O blood are universal donors"
   - type O, group O
    
2. A nonmetallic bivalent element that is normally a colourless odourless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust
   - oxygen, atomic number 8

Derived forms: ossa, ora

Type of: alphabetic character, blood group, blood type, chemical element, computer software, connective tissue, element, eye, gas, letter, letter of the alphabet, metal, metallic element, oculus, opening, optic, orifice, package, porta, software, software package, software program, software system

Part of: air, endoskeleton, H2O, horn, Latin alphabet, ozone, platform, Roman alphabet, water

Encyclopedia: O O, Yeah! Ultimate Aerosmith Hits O, ce veste minunata O, Vrba O, Yeah! The Ultimate Aerosmith Hits O, the Oprah Magazine O,p'-DDD O, ce veste minunata! O, ce veste minunată! O, The Oprah Magazine O, Canada O, Denmark O, Brother, Where Art Thou? O, Brother Where Art Thou? O, Little Town of Bethlehem O, Sailor O, Draconian Devil! O, Fortuna