Source : Webster's Revised Unabridged Dictionary (1913)

Hydrodynamic \Hy`dro*dy*nam"ic\, Hydrodynamical
\Hy`dro*dy*nam"ic*al\, a. [Hydro-, 1 + dynamic, -ical: cf. F.
   hydrodynamique.]
   Pertaining to, or derived from, the dynamical action of water
   of a liquid; of or pertaining to water power.

   {Hydrodynamic friction}, friction produced by the viscosity
      of a liquid in motion.