Source : Webster's Revised Unabridged Dictionary (1913)

Plowshare \Plow"share`\, Ploughshare \Plough"share"\, n.
   The share of a plow, or that part which cuts the slice of
   earth or sod at the bottom of the furrow.

   {Plowshare bone} (Anat.), the pygostyle.

Source : WordNet®

plowshare
     n : a sharp steel wedge that cuts loose the top layer of soil
         [syn: {ploughshare}, {share}]