Source : Webster's Revised Unabridged Dictionary (1913)

Jag \Jag\, v. t. [imp. & p. p. {Jagged}; p. pr. & vb. n.
   {Jagging}.]
   To cut into notches or teeth like those of a saw; to notch.
   [Written also {jagg}.]

   {Jagging iron}, a wheel with a zigzag or jagged edge for
      cutting cakes or pastry into ornamental figures.