Source : Webster's Revised Unabridged Dictionary (1913)

Expanse \Ex*panse"\, v. t.
   To expand. [Obs.]

         That lies expansed unto the eyes of all. --Sir. T.
                                                  Browne.

Expanse \Ex*panse"\, n. [From L. expansus, p. p. of expandere.
   See {Expand}.]
   That which is expanded or spread out; a wide extent of space
   or body; especially, the arch of the sky. ``The green
   expanse.'' --Savage.

         Lights . . . high in the expanse of heaven. --Milton.

         The smooth expanse of crystal lakes.     --Pope.

Source : WordNet®

expanse
     n 1: a wide scope; "the sweep of the plains" [syn: {sweep}]
     2: the extent of a 2-dimensional surface enclosed within a
        boundary; "the area of a rectangle"; "it was about 500
        square feet in area" [syn: {area}, {surface area}]
     3: a wide and open space or area as of surface or land or sky