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"cutting tooth," 1670s, from Medieval Latin incisor "a cutting tooth," literally "that which cuts into," from Latin incisus, past participle of incidere (see incision). Inscisours as the name of a cutting tool is attested from early 15c.
incisor in·ci·sor (ĭn-sī'zər)
Any of the four teeth adapted for cutting or gnawing, having a chisel-shaped crown and a single conical root and located in the front part of both jaws in both deciduous and permanent dentitions.