ploughshare

from WordNet (r) 3.0 (2006)

ploughshare
    n 1: a sharp steel wedge that cuts loose the top layer of soil
         [syn: {plowshare}, {ploughshare}, {share}]

from The Collaborative International Dictionary of English v.0.48

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.
   [1913 Webster]

   {Plowshare bone} (Anat.), the pygostyle.
      [1913 Webster] Plowtail