Autogiro is the term trademarked by Cierva. Configuration (pusher as Buhl Autogiro or tractor as in C.30) is irrelevant.

Autogyro, gyroplane, gyrocopter, rotaplane, are all generic terms defining Autogiro-type aircraft.

“Autogyro” is an alternate spelling of “Autogiro” to avoid violating Cierva’s trademark.

“Gyroplane” appears very soon after after Cierva’s 1925 demonstrarton of the C.6 at Farnborough as will be verified by perusing official reports available at the UK National Archives.

“Gyrocopter” has been around for a long time and predates Bensen’s use. E.B. Wilford of rigid feathering rotor – equipped WRK gyroplane fame used the term in the 1940s.

“Rotaplane” was used by the Air Ministry to avoid appearance of favouritism towards any particular manufacturer, e.g. Cierva Autogiro, Hafner Gyroplane, Wilford Gyrocopter, etc.