The Collaborative International Dictionary
Hydrodynamical
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.
Wiktionary
hydrodynamical
a. hydrodynamic