n. 犁刀

[ noun ]
a sharp steel wedge that precedes the plow and cuts vertically through the soil
<noun.artifact>

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}.]