• Oculus
    A circular or eye shaped window.
  • Ogive
    Diagonal arch which outlines the ribs of the vault of a bay (divided into four or six parts).
  • Opening
    Window or opening in a wall.
  • Opus sectile
    Inlaid, mosaic decoration (often in marble).
  • Opus spicatum
    Small tool cut on the diagonal used during the pre-Roman era.
  • Ovum
    Egg-shaped ornamental motif.