Source : Webster's Revised Unabridged Dictionary (1913)

Moldboard \Mold"board`\, Mouldboard \Mould"board`\, n.
   1. A curved plate of iron (originally of wood) back of the
      share of a plow, which turns over the earth in plowing.

   2. (Founding) A follow board.

Source : WordNet®

moldboard
     n : wedge formed by the curved part of a steel plow blade that
         turns the furrow [syn: {mouldboard}]