The Collaborative International Dictionary of English v.0.48:

Developable \De*vel"op*a*ble\, a.
   Capable of being developed. --J. Peile.
   [1913 Webster]

   Developable surface (Math.), a surface described by a
      moving right line, and such that consecutive positions of
      the generator intersect each other. Hence, the surface can
      be developed into a plane.
      [1913 Webster]