Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

            The flowery roof Showered roses, which the morn
            repaired.                             --Milton.

   3. (Mining.) The surface or bed of rock immediately overlying
      a bed of coal or a flat vein.

   {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.

French \French\ (fr[e^]nch), a. [AS. frencisc, LL. franciscus,
   from L. Francus a Frank: cf. OF. franceis, franchois,
   fran[,c]ois, F. fran[,c]ais. See {Frank}, a., and cf.
   {Frankish}.]
   Of or pertaining to France or its inhabitants.

   {French bean} (Bot.), the common kidney bean ({Phaseolus
      vulgaris}).

   {French berry} (Bot.), the berry of a species of buckthorn
      ({Rhamnus catharticus}), which affords a saffron, green or
      purple pigment.

   {French casement} (Arch.) See {French window}, under
      {Window}.

   {French chalk} (Min.), a variety of granular talc; -- used
      for drawing lines on cloth, etc. See under {Chalk}.

   {French cowslip} (Bot.) The {Primula Auricula}. See
      {Bear's-ear}.

   {French fake} (Naut.), a mode of coiling a rope by running it
      backward and forward in parallel bends, so that it may run
      freely.

   {French honeysuckle} (Bot.) a plant of the genus {Hedysarum}
      ({H. coronarium}); -- called also {garland honeysuckle}.
      

   {French horn}, a metallic wind instrument, consisting of a
      long tube twisted into circular folds and gradually
      expanding from the mouthpiece to the end at which the
      sound issues; -- called in France {cor de chasse}.

   {French leave}, an informal, hasty, or secret departure;
      esp., the leaving a place without paying one's debts.

   {French pie} [French (here used in sense of ``foreign'') +
      pie a magpie (in allusion to its black and white color)]
      (Zo["o]l.), the European great spotted woodpecker
      ({Dryobstes major}); -- called also {wood pie}.

   {French polish}.
   (a) A preparation for the surface of woodwork, consisting of
       gums dissolved in alcohol, either shellac alone, or
       shellac with other gums added.
   (b) The glossy surface produced by the application of the
       above.

   {French purple}, a dyestuff obtained from lichens and used
      for coloring woolen and silken fabrics, without the aid of
      mordants. --Ure.

   {French red} rouge.

   {French rice}, amelcorn.

   {French roof} (Arch.), a modified form of mansard roof having
      a nearly flat deck for the upper slope.

   {French tub}, a dyer's mixture of protochloride of tin and
      logwood; -- called also {plum tub}. --Ure.

   {French window}. See under {Window}.

Source : WordNet®

French roof
     n : a mansard roof with sides that are nearly perpendicular