coulter
Concise Oxford English Dictionary © 2008 Oxford University Press:
coulter /ˈkəʊltə/ (US colter)
▶noun a vertical cutting blade fixed in front of a ploughshare.
■ the part of a seed drill that makes the furrow for the seed.
– origin OE, from L. culter ‘knife or ploughshare’.
'coulter' also found in these Oxford entries:

