Source : Webster's Revised Unabridged Dictionary (1913)

Boundary \Bound"a*ry\, n.; pl. {Boundaries} [From {Bound} a
   limit; cf. LL. bonnarium piece of land with fixed limits.]
   That which indicates or fixes a limit or extent, or marks a
   bound, as of a territory; a bounding or separating line; a
   real or imaginary limit.

         But still his native country lies Beyond the boundaries
         of the skies.                            --N. Cotton.

         That bright and tranquil stream, the boundary of Louth
         and Meath.                               --Macaulay.

         Sensation and reflection are the boundaries of our
         thoughts.                                --Locke.

   Syn: Limit; bound; border; term; termination; barrier; verge;
        confines; precinct.

   Usage: {Bound}, {Boundary}. Boundary, in its original and
          strictest sense, is a visible object or mark
          indicating a limit. Bound is the limit itself. But in
          ordinary usage the two words are made interchangeable.

Source : WordNet®

boundary
     n 1: the line or plane indicating the limit or extent of
          something [syn: {bound}, {bounds}]
     2: a line determining the limits of an area [syn: {edge}, {bound}]
     3: the greatest possible degree of something; "what he did was
        beyond the bounds of acceptable behavior"; "to the limit
        of his ability" [syn: {limit}, {bounds}]