Source : Webster's Revised Unabridged Dictionary (1913)

Hydrodynamics \Hy`dro*dy*nam"ics\, n. [Hydro-, 1 + dynamics: cf.
   F. hydrodynamique.]
   That branch of the science of mechanics which relates to
   fluids, or, as usually limited, which treats of the laws of
   motion and action of nonelastic fluids, whether as
   investigated mathematically, or by observation and
   experiment; the principles of dynamics, as applied to water
   and other fluids.

   Note: The word is sometimes used as a general term, including
         both hydrostatics and hydraulics, together with
         pneumatics and acoustics. See {Hydraulics}.

Source : WordNet®

hydrodynamics
     n : study of fluids in motion [syn: {hydrokinetics}]