Source : Webster's Revised Unabridged Dictionary (1913)

Ashlar \Ash"lar\, Ashler \Ash"ler\, n. [OE. ascheler, achiler,
   OF. aiseler, fr. aiselle, dim. of ais plank, fr. L. axis,
   assis, plank, axle. See {Axle}.]
   1. (Masonry)
      (a) Hewn or squared stone; also, masonry made of squared
          or hewn stone.

                Rough ashlar, a block of freestone as brought
                from the quarry. When hammer-dressed it is known
                as common ashlar.                 --Knight.
      (b) In the United States especially, a thin facing of
          squared and dressed stone upon a wall of rubble or
          brick. --Knight.

Source : WordNet®

ashlar
     n : a rectangular block of hewn stone used for building purposes