The Collaborative International Dictionary of English v.0.48:

Jagger \Jag"ger\, n. [From 4th Jag.]
   One who, or that which, jags; specifically:
   (a) a jagging iron used for crimping pies, cakes, etc.
   (b) A toothed chisel. See Jag, v. t.
       [1913 Webster]

   Jagger spring, a spring beneath a seat, and resting on
      cleats or blocks in the body of a vehicle. --Knight.
      [1913 Webster]