The Collaborative International Dictionary of English v.0.48:

Mural \Mu"ral\, a. [F., fr. L. muralis, fr. murus wall. See
   Mure a wall.]
   1. Of or pertaining to a wall; being on, or in, a wall;
      growing on, or against, a wall; as, a mural quadrant.
      "Mural breach." --Milton. "Mural fruit." --Evelyn.
      [1913 Webster]

   2. Resembling a wall; perpendicular or steep; as, a mural
      precipice.
      [1913 Webster]

   Mural circle (Astron.), a graduated circle, in the plane of
      the meridian, attached permanently to a perpendicular
      wall; -- used for measuring arcs of the meridian. See
      Circle, n., 3.

   Mural crown (Rom. Antiq.), a golden crown, or circle of
      gold indented so as to resemble a battlement, bestowed on
      him who first mounted the wall of a besieged place, and
      there lodged a standard.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mural
    adj 1: of or relating to walls; "mural painting"
    n 1: a painting that is applied to a wall surface [syn: mural,
         wall painting]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "mural":
   abstract, abstraction, altarpiece, block print, collage,
   color print, copy, cyclorama, daub, diptych, engraving, fresco,
   icon, illumination, illustration, image, likeness, miniature,
   montage, mosaic, panorama, parietal, partitioned, photograph,
   picture, print, representation, reproduction, septal,
   stained glass window, stencil, still life, tableau, tapestry,
   triptych, wall painting, walled