Hy″dro‐plane (?), n. [Pref. hydro-, 1 + plane.] 1. A plane, or any of a number of planes, projecting from the hull of a submarine boat, which by being elevated or depressed cause the boat, when going ahead, to sink or rise, after the manner of an aëroplane.
2. A projecting plane or fin on a gliding boat to lift the moving boat on top of the water; also, a gliding boat.