Source : Webster's Revised Unabridged Dictionary (1913)

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.