The Collaborative International Dictionary of English v.0.48:

Dowel \Dow"el\, n. [Cf. G. d["o]bel peg, F. douelle state of a
   cask, surface of an arch, douille socket, little pipe,
   cartridge.] (Mech.)
   1. A pin, or block, of wood or metal, fitting into holes in
      the abutting portions of two pieces, and being partly in
      one piece and partly in the other, to keep them in their
      proper relative position.
      [1913 Webster]

   2. A piece of wood driven into a wall, so that other pieces
      may be nailed to it.
      [1913 Webster]

   Dowel joint, a joint secured by a dowel or dowels.

   Dowel pin, a dowel. See Dowel, n., 1.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dowel pin
    n 1: a fastener that is inserted into holes in two adjacent
         pieces and holds them together [syn: dowel, dowel pin,
         joggle]