The Collaborative International Dictionary of English v.0.48:

Rewel bone \Rew"el bone`\ [Perh. from F. rouelle, dim. of roue a
   wheel, L. rota.]
   An obsolete phrase of disputed meaning, -- perhaps, smooth or
   polished bone.
   [1913 Webster]

         His saddle was of rewel boon.            --Chaucer.
   [1913 Webster]