The Collaborative International Dictionary of English v.0.48:

Renal \Re"nal\ (r[=e]"nal), a. [L. renalis, fr. renes the
   kidneys or reins: cf. F. r['e]nal. See Reins.] (Anat.)
   Of or pertaining to the kidneys; in the region of the
   kidneys.
   [1913 Webster]

   Renal capsules or Renal glands, the suprarenal capsules.
      See under Capsule.

   Renal casts, Renal colic. (Med.) See under Cast, and
      Colic.
      [1913 Webster]

WordNet (r) 3.0 (2006):

renal
    adj 1: of or relating to the kidneys [syn: nephritic, renal]