Cock \Cock\, n. [It. cocca notch of an arrow.] 1. The notch of an arrow or crossbow. 2. The hammer in the lock of a firearm. {At cock}, {At full cock}, with the hammer raised and ready to fire; -- said of firearms, also, jocularly, of one prepared for instant action. {At half cock}. See under {Half}. {Cock feather} (Archery), the feather of an arrow at right angles to the direction of the cock or notch. --Nares.