The Collaborative International Dictionary of English v.0.48:

Hydragogue \Hy"dra*gogue\, a. [L. hydragogus conveying off
   water, Gr. ?; "y`dwr water + ? to lead: cf. F. hydragogue.]
   (Med.)
   Causing a discharge of water; expelling serum effused into
   any part of the body, as in dropsy. -- n. A hydragogue
   medicine, usually a cathartic or diuretic.
   [1913 Webster]