Source : Webster's Revised Unabridged Dictionary (1913)

Ferrule \Fer"rule\ (? or ?; 277), n. [Formerly verrel, F.
   virole, fr. L. viriola little bracelet, dim. of viriae, pl.,
   bracelets; prob. akin to viere to twist, weave, and E. withe.
   The spelling with f is due to confusion with L. ferrum iron.]
   1. A ring or cap of metal put round a cane, tool, handle, or
      other similar object, to strengthen it, or prevent
      splitting and wearing.

   2. (Steam Boilers) A bushing for expanding the end of a flue
      to fasten it tightly in the tube plate, or for partly
      filling up its mouth.

Source : WordNet®

ferrule
     n : a metal cap or band placed on a wooden pole to prevent
         splitting [syn: {collet}]