Camber arch

from WordNet (r) 3.0 (2006)

camber arch
    n 1: an arch with a straight horizontal extrados and a slightly
         arched intrados

from The Collaborative International Dictionary of English v.0.48

Camber \Cam"ber\, n. [Of. cambre bent, curved; akin to F.
   cambrer to vault, to bend, fr. L. camerare to arch over, fr.
   camera vault, arch. See {Chamber}, and cf. {Camerate}.]
   1. (Shipbuilding) An upward convexity of a deck or other
      surface; as, she has a high camber (said of a vessel
      having an unusual convexity of deck).
      [1913 Webster]

   2. (Arch.) An upward concavity in the under side of a beam,
      girder, or lintel; also, a slight upward concavity in a
      straight arch. See {Hogback}.
      [1913 Webster]

   {Camber arch} (Arch.), an arch whose intrados, though
      apparently straight, has a slightly concave curve upward.
      

   {Camber beam} (Arch.), a beam whose under side has a concave
      curve upward.
      [1913 Webster]