The Collaborative International Dictionary of English v.0.48:

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.
          [1913 Webster]

                Rough ashlar, a block of freestone as brought
                from the quarry. When hammer-dressed it is known
                as common ashlar.                 --Knight.
          [1913 Webster]
      (b) In the United States especially, a thin facing of
          squared and dressed stone upon a wall of rubble or
          brick. --Knight.
          [1913 Webster] Ashlaring

WordNet (r) 3.0 (2006):

ashlar
    n 1: a rectangular block of hewn stone used for building
         purposes