The Collaborative International Dictionary of English v.0.48:

welt \welt\ (w[e^]lt), n. [OE. welte, probably fr. W. gwald a
   hem, a welt, gwaldu to welt or to hem.]
   [1913 Webster]
   1. That which, being sewed or otherwise fastened to an edge
      or border, serves to guard, strengthen, or adorn it; as:
      (a) A small cord covered with cloth and sewed on a seam or
          border to strengthen it; an edge of cloth folded on
          itself, usually over a cord, and sewed down.
      (b) A hem, border, or fringe. [Obs.]
      (c) In shoemaking, a narrow strip of leather around a
          shoe, between the upper leather and sole.
      (d) In steam boilers and sheet-iron work, a strip riveted
          upon the edges of plates that form a butt joint.
      (e) In carpentry, a strip of wood fastened over a flush
          seam or joint, or an angle, to strengthen it.
      (f) In machine-made stockings, a strip, or flap, of which
          the heel is formed.
          [1913 Webster]

   2. (Her.) A narrow border, as of an ordinary, but not
      extending around the ends.
      [1913 Webster]

   3. A raised ridge on the surface of the skin, produced by a
      blow, as from a stick or whip; a wale; a weal; as, to
      raise welts on the back with a whip.

   Syn: wale; weal; wheal.
        [PJC]

   4. A blow that produces a welt[3].
      [PJC]

   Welt joint, a joint, as of plates, made with a welt,
      instead of by overlapping the edges. See Weld, n., 1
      (d) .
          [1913 Webster]