The Collaborative International Dictionary of English v.0.48:

Lithagogue \Lith"a*gogue\ (l[i^]th"[.a]*g[o^]g), n. [Gr. li`qos
   stone + 'agwgo`s leading.] (Med.)
   A medicine having, or supposed to have, the power of
   expelling calculous matter with the urine. --Hooper.
   [1913 Webster]