The Collaborative International Dictionary of English v.0.48:

Defilading \De`fi*lad"ing\, n. (Mil.)
   The art or act of determining the directions and heights of
   the lines of rampart with reference to the protection of the
   interior from exposure to an enemy's fire from any point
   within range, or from any works which may be erected.
   --Farrow.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Defilade \De`fi*lade"\, v. t. [imp. & p. p. Defiladed; p. pr.
   & vb. n. Defilading.] [Cf. F. d['e]filer to defile, and
   d['e]filade act of defiling. See 1st Defile.] (Mil.)
   To raise, as a rampart, so as to shelter interior works
   commanded from some higher point.
   [1913 Webster]