Old English culter, from Latin culter "a knife, iron blade in a plowshare," from PIE root *(s)kel- "to cut" (see scale (n.1)). As a surname (13c.), probably from Coulter in Lancashire.
(1 Sam. 13:20, 21), an agricultural instrument, elsewhere called "ploughshare" (Isa. 2:4; Micah 4:3; Joel 3:10). It was the facing-piece of a plough, analogous to the modern coulter.