Source : Webster's Revised Unabridged Dictionary (1913)

Mortar \Mor"tar\, n. [OE. mortier, F. mortier, L. mortarium
   mortar, a large basin or trough in which mortar is made, a
   mortar (in sense 1, above). See 1st {Mortar}.] (Arch.)
   A building material made by mixing lime, cement, or plaster
   of Paris, with sand, water, and sometimes other materials; --
   used in masonry for joining stones, bricks, etc., also for
   plastering, and in other ways.

   {Mortar bed}, a shallow box or receptacle in which mortar is
      mixed.

   {Mortar board}.
   (a) A small square board with a handle beneath, for holding
       mortar; a hawk.
   (b) A cap with a broad, projecting, square top; -- worn by
       students in some colleges. [Slang]

Mortar \Mor"tar\, n. [OE. morter, AS. mort[=e]re, L. mortarium:
   cf. F. mortier mortar. Cf. sense 2 (below), also 2d {Mortar},
   {Martel}, {Morter}.]
   1. A strong vessel, commonly in form of an inverted bell, in
      which substances are pounded or rubbed with a pestle.

   2. [F. mortier, fr. L. mortarium mortar (for trituarating).]
      (Mil.) A short piece of ordnance, used for throwing bombs,
      carcasses, shells, etc., at high angles of elevation, as
      45[deg], and even higher; -- so named from its resemblance
      in shape to the utensil above described.

   {Mortar bed} (Mil.), a framework of wood and iron, suitably
      hollowed out to receive the breech and trunnions of a
      mortar.

   {Mortar boat} or {vessel} (Naut.), a boat strongly built and
      adapted to carrying a mortar or mortars for bombarding; a
      bomb ketch.

   {Mortar piece}, a mortar. [Obs.] --Shak.

Mortar \Mor"tar\, v. t.
   To plaster or make fast with mortar.

Mortar \Mor"tar\, n. [F. mortier. See {Mortar} a vessel.]
   A chamber lamp or light. [Obs.] --Chaucer.

Source : WordNet®

mortar
     n 1: a muzzle-loading high-angle gun with a short barrel that
          fires shells at high elevations for a short range [syn:
          {howitzer}, {trench mortar}]
     2: used as a bond in masonry or for covering a wall
     3: a bowl-shaped vessel in which substances can be ground and
        mixed with a pestle
     v : plaster with mortar; "mortar the wall"