Noah Webster's Dictionary (n.) A knife or cutter, attached to the beam of a plow to cut the sward, in advance of the plowshare and moldboard.

Multi-Version Concordance Colter (1 Occurrence) 1 Samuel 13:20 But all the Israelites went down to the Philistines, to sharpen every man his share, and his colter, and his ax, and his mattock. (WBS)