The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   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.
      [1913 Webster]

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

   Mortar boat or Mortar 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.
      [1913 Webster]