"cutting tooth," 1670s, from Medieval Latin incisor "a cutting tooth," literally "that which cuts into," from Latin incisus, past participle of incīdere "to cut, cut through, cut open; engrave," from in- "into, in, on, upon" (from PIE root *en "in") + -cidere, combining form of caedere "to cut" (from PIE root *kae-id- "to strike"). Inscisours as the name of a cutting tool is attested from early 15c. Related: Incisorial.