The Collaborative International Dictionary of English v.0.48:

Jointer \Joint"er\, n.
   1. One who, or that which, joints.
      [1913 Webster]

   2. A plane for smoothing the surfaces of pieces which are to
      be accurately joined; especially:
      (a) The longest plane used by a joiner.
      (b) (Coopering) A long stationary plane, for planing the
          edges of barrel staves.
          [1913 Webster]

   3. (Masonry)
      (a) A bent piece of iron inserted to strengthen the joints
          of a wall.
      (b) A tool for pointing the joints in brickwork.
          [1913 Webster]

WordNet (r) 3.0 (2006):

jointer
    n 1: a long carpenter's plane used to shape the edges of boards
         so they will fit together [syn: jointer, jointer plane,
         jointing plane, long plane]