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]