Source : Webster's Revised Unabridged Dictionary (1913)

Halfcock \Half"cock`\, v. t. [imp. & p. p. {Halfcocked}; p. pr.
   & vb. n. {Halfcocking}.]
   To set the cock of (a firearm) at the first notch.

   {To go off halfcocked}.
   (a) To be discharged prematurely, or with the trigger at half
       cock; -- said of a firearm.
   (b) To do or say something without due thought or care.
       [Colloq. or Low]