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 ]

n. The study of the interaction of magnetic fields with electrically conductive fluids, such as a plasma or a molten metal. [ WordNet 1.5 ]