{ } 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. [ 1913 Webster ]

Hydrodynamic friction, friction produced by the viscosity of a liquid in motion. [ 1913 Webster ]

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. [ 1913 Webster ]

☞ The word is sometimes used as a general term, including both hydrostatics and hydraulics, together with pneumatics and acoustics. See Hydraulics. [ 1913 Webster ]