The Collaborative International Dictionary of English v.0.48:

Roof \Roof\, n. [OE. rof, AS. hr?f top, roof; akin to D. roef
   cabin, Icel. hr?f a shed under which ships are built or kept;
   cf. OS. hr?st roof, Goth. hr?t. Cf. Roost.]
   1. (Arch.) The cover of any building, including the roofing
      (see Roofing) and all the materials and construction
      necessary to carry and maintain the same upon the walls or
      other uprights. In the case of a building with vaulted
      ceilings protected by an outer roof, some writers call the
      vault the roof, and the outer protection the roof mask. It
      is better, however, to consider the vault as the ceiling
      only, in cases where it has farther covering.
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   2. That which resembles, or corresponds to, the covering or
      the ceiling of a house; as, the roof of a cavern; the roof
      of the mouth.
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            The flowery roof
            Showered roses, which the morn repaired. --Milton.
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   3. (Mining.) The surface or bed of rock immediately overlying
      a bed of coal or a flat vein.
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   Bell roof, French roof, etc. (Arch.) See under Bell,
      French, etc.

   Flat roof. (Arch.)
      (a) A roof actually horizontal and level, as in some
          Oriental buildings.
      (b) A roof nearly horizontal, constructed of such material
          as allows the water to run off freely from a very
          slight inclination.

   Roof plate. (Arch.) See Plate, n., 10.
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