Source : Webster's Revised Unabridged Dictionary (1913)

Jag \Jag\, n. [Prob. of Celtic origin; cf. W. gag aperture,
   cleft, chink; akin to Ir. & Gael. gag.] [Written also
   {jagg}.]
   1. A notch; a cleft; a barb; a ragged or sharp protuberance;
      a denticulation.

            Arethuss arose . . . From rock and from jag.
                                                  --Shelley.

            Garments thus beset with long jags.   --Holland.

   2. A part broken off; a fragment. --Bp. Hacket.

   3. (Bot.) A cleft or division.

   {Jag bolt}, a bolt with a nicked or barbed shank which
      resists retraction, as when leaded into stone.