I. ˈ ̷ ̷ ̷ ̷ at hydro- +ˌ- noun
Etymology: hydr- + plane
1. : a hydrofoil or any surface (as of an airplane pontoon) having a similar shape and tendency
2.
a. : a speedboat equipped with hydrofoils or having a stepped bottom that provides more than one lifting surface so that the hull is raised wholly or partially out of the water as the boat attains forward speed
b. : diving plane
3. : seaplane — not used technically
II. intransitive verb
1. : to skim over the water with the hull either clear of the surface or barely immersed
2. : to drive or ride in a hydroplane
III. intransitive verb
of a vehicle or tire : to ride supported by a film of water on a wet surface when a critical speed is reached with a resultant loss of directional stability and braking effectiveness