nock (n.)

"a notch," specifically, in archery, "the notch on the horn of a bow," where the string is fastened, also "notch on the end of an arrow," which rests on the string, late 14c., nokke, a word of uncertain origin, probably from a Scandinavian source (such as Swedish nock "notch"), or a continental Germanic one such as Low German nokk, Middle Dutch nocke, Dutch nok "tip of a sail" or other similar words denoting projections or tips. Perhaps connected to nook.

mid-14c., "make a notch in;" 1510s, "fit (the nock of an arrow) to a bowstring;" from nock (n.). Related: Nocked; nocking.