The Collaborative International Dictionary of English v.0.48:

Renal calculus \Renal calculus\ (Med.),
   an abnormal concretion formed in the excretory passages of
   the kidney, composed primarily of calcium oxalates and
   phosphates; -- also called kidney stone, nephrolith, and
   nephritic calculus (an obsolete term).
   [PJC]

WordNet (r) 3.0 (2006):

renal calculus
    n 1: a calculus formed in the kidney [syn: kidney stone,
         urinary calculus, nephrolith, renal calculus]