The Collaborative International Dictionary of English v.0.48:

Cystolith \Cys"to*lith\ (s?s"t?-l?th), n. [Gr. ???? bladder +
   -lith.]
   1. (Bot.) A concretion of mineral matter within a leaf or
      other part of a plant.
      [1913 Webster]

   2. (Med.) A urinary calculus.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cystolith
    n 1: a calculus formed in the bladder [syn: bladder stone,
         cystolith]