资料来源 : Webster's Revised Unabridged Dictionary (1913)

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.

         His saddle was of rewel boon.            --Chaucer.