The Collaborative International Dictionary of English v.0.48:

Mortise \Mor"tise\, n. [F. mortaise; cf. Sp. mortaja, Ar.
   murtazz fixed, or W. mortais, Ir. mortis, moirtis, Gael.
   moirteis.]
   A cavity cut into a piece of timber, or other material, to
   receive something (as the end of another piece) made to fit
   it, and called a tenon.
   [1913 Webster]

   Mortise and tenon (Carp.), made with a mortise and tenon;
      joined or united by means of a mortise and tenon; -- used
      adjectively.

   Mortise joint, a joint made by a mortise and tenon.

   Mortise lock. See under Lock.

   Mortise wheel, a cast-iron wheel, with wooden clogs
      inserted in mortises on its face or edge; -- also called
      mortise gear, and core gear.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mortise \Mor"tise\, v. t. [imp. & p. p. Mortised; p. pr. & vb.
   n. Mortising.]
   1. To cut or make a mortise in.
      [1913 Webster]

   2. To join or fasten by a tenon and mortise; as, to mortise a
      beam into a post, or a joist into a girder.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mortise
    n 1: a square hole made to receive a tenon and so to form a
         joint [syn: mortise, mortice]
    v 1: cut a hole for a tenon in [syn: mortise, mortice]
    2: join by a tenon and mortise [syn: mortice, mortise]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "mortise":
   ankle, articulate, articulation, batten, batten down, bolt,
   boundary, buckle, butt, button, cervix, clasp, cleat, clinch, clip,
   closure, coact, connecting link, connecting rod, connection,
   cooperate, coupling, dovetail, elbow, embrace, engage,
   gliding joint, hasp, hinge, hinged joint, hip, hitch, hook,
   interact, interchange, interface, interlace, intermesh, interplay,
   intertwine, interweave, interwork, jam, join, joining, joint,
   juncture, knee, knuckle, latch, link, lock, mesh, miter, nail,
   neck, peg, pin, pivot, pivot joint, rabbet, rivet, scarf, screw,
   seam, sew, shoulder, skewer, snap, staple, stick, stitch, suture,
   symphysis, tack, tie rod, toggle, toggle joint, union, wedge, weld,
   wrist, zipper