The Collaborative International Dictionary of English v.0.48:

Miter \Mi"ter\, Mitre \Mi"tre\, n. [F. mitre, fr. L. mitra
   headband, turban, Gr. ?.]
   1. A covering for the head, worn on solemn occasions by
      bishops and other church dignitaries. It has been made in
      many forms, the present form being a lofty cap with two
      points or peaks. --Fairholt.
      [1913 Webster]

   2. The surface forming the beveled end or edge of a piece
      where a miter joint is made; also, a joint formed or a
      junction effected by two beveled ends or edges; a miter
      joint.
      [1913 Webster]

   3. (Numis.) A sort of base money or coin.
      [1913 Webster]

   Miter box (Carp. & Print.), an apparatus for guiding a
      handsaw at the proper angle in making a miter joint; esp.,
      a wooden or metal trough with vertical kerfs in its
      upright sides, for guides.

   Miter dovetail (Carp.), a kind of dovetail for a miter
      joint in which there is only one joint line visible, and
      that at the angle.

   Miter gauge (Carp.), a gauge for determining the angle of a
      miter.

   Miter joint, a joint formed by pieces matched and united
      upon a line bisecting the angle of junction, as by the
      beveled ends of two pieces of molding or brass rule, etc.
      The term is used especially when the pieces form a right
      angle, such as the edges of a window frame, and the edge
      of each piece at the point of junction is cut at a 45[deg]
      angle to its long direction. See Miter, 2.

   Miter shell (Zool.), any one of numerous species of marine
      univalve shells of the genus Mitra.

   Miter square (Carp.), a bevel with an immovable arm at an
      angle of 45[deg], for striking lines on stuff to be
      mitered; also, a square with an arm adjustable to any
      angle.

   Miter wheels, a pair of bevel gears, of equal diameter,
      adapted for working together, usually with their axes at
      right angles.
      [1913 Webster] Miter

The Collaborative International Dictionary of English v.0.48:

Miter \Mi"ter\, Mitre \Mi"tre\, v. t. [imp. & p. p. Miteredor
   Mitred; p. pr. & vb. n. Miteringor Mitring.]
   1. To place a miter upon; to adorn with a miter. [WordNet
      sense 2] "Mitered locks." --Milton.
      [1913 Webster]

   2. To match together, as two pieces of molding or brass rule
      on a line bisecting the angle of junction; to fit together
      in a miter joint. [WordNet sense 3]
      [1913 Webster]

   3. To bevel the ends or edges of, for the purpose of matching
      together at an angle. [WordNet sense 1]
      [1913 Webster] Miter

The Collaborative International Dictionary of English v.0.48:

Miter \Mi"ter\, Mitre \Mi"tre\, v. i.
   To meet and match together, as two pieces of molding, on a
   line bisecting the angle of junction.
   [1913 Webster]

WordNet (r) 3.0 (2006):

miter
    n 1: joint that forms a corner; usually both sides are bevelled
         at a 45-degree angle to form a 90-degree corner [syn:
         miter joint, mitre joint, miter, mitre]
    2: the surface of a beveled end of a piece where a miter joint
       is made; "he covered the miter with glue before making the
       joint" [syn: miter, mitre]
    3: a liturgical headdress worn by bishops on formal occasions
       [syn: miter, mitre]
    v 1: bevel the edges of, to make a miter joint
    2: confer a miter on (a bishop)
    3: fit together in a miter joint