Hydro-aeroplane \Hy"dro-a"["e]r*o*plane`\ (A["e]ronautics)
An a["e]roplane with a boatlike or other understructure that
enables it to travel on, or to rise from the surface of, a
body of water by its own motive power; -- now usually
referred to as a {seaplane}. [obsolescent]
[Webster 1913 Suppl. +PJC]