late 14c., "a cutting made in surgery," from Old French incision (13c.) and directly from Latin incisionem (nominative incisio) "a cutting into," recorded only in figurative senses, noun of action from past-participle stem of incīdere "to cut, cut through, cut open," 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"). Meaning "act of cutting into" is from early 15c.
early 15c., inscisif, "slashing, cutting with a sharp edge," from Old French incisif (medical) "invasive, effective," and directly from Medieval Latin incisivus, from Latin incis-, past participle stem of incīdere "to cut into" (see incision). Originally literal; figurative sense of "mentally acute, sharply and clearly expressive" first recorded 1850 as a borrowing from French. Related: Incisively; incisiveness.
*kaə-id-, Proto-Indo-European root meaning "to strike."
It forms all or part of: abscise; avicide; biocide; caesarian; caesura; cement; chisel; -cide; circumcise; circumcision; concise; decide; decision; deicide; excise (v.); excision; felicide; feticide; filicide; floricide; fratricide; fungicide; gallinicide; genocide; germicide; herbicide; homicide; incise; incision; incisor; infanticide; insecticide; legicide; liberticide; libricide; matricide; parricide; patricide; pesticide; precise; precision; prolicide; scissors; senicide; spermicide; suicide; uxoricide; verbicide.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit skhidati "beats, tears;" Latin caedere "to strike down, fell, slay;" Lithuanian kaišti "shave;" Armenian xait'em "to stab;" Albanian qeth "to shave;" Middle Dutch heien "to drive piles," Old High German heia "wooden hammer," German heien "beat."