A (US:) colter / (British:) coulter (Latin 'culter' = 'knife') is a vertically mounted component of many ploughs that cuts an edge about 7 inches (18 cm) deep ahead of a plowshare.
[3][1] In 2011 an early medieval coulter was excavated from a site in Kent, England.
[6][1] Its advantage was a smoothly cut bank, and it sliced plant debris to the width of the furrow.
[2] In his 1854 book, Henry Stephens used dynamometer measurements to conclude that a plough without a coulter took about the same amount of force to pull but using a coulter resulted in a much cleaner result.
[1] It softens the soil, allowing the plough to undercut the furrow made by the coulter.