Colter

from WordNet (r) 3.0 (2006)

colter
    n 1: a sharp steel wedge that precedes the plow and cuts
         vertically through the soil [syn: {colter}, {coulter}]

from The Collaborative International Dictionary of English v.0.48

Colter \Col"ter\, n. [AS. culter, fr. L. culter plowshare,
   knife. Cf. {Cutlass}.]
   A knife or cutter, attached to the beam of a plow to cut the
   sward, in advance of the plowshare and moldboard. [Written
   also {coulter}.]
   [1913 Webster]