We are certainly using different definitons for the term clutch.
I take it to mean a component whereby (either manually or automatically) the engine can be disconnected from and reconnected to the output shaft to permit the engine to rotate without rotating the output shaft.
A freewheel unit is a component which permits the output shaft (and rotors) to turn while the engine is not.
Most bicycle rear wheels contain a freewheel unit, but most people would never call it a clutch.
If you look at the context in which the term clutch has been used by others in this thread, I think that you will find that it is more in keeping with my defibnition, than with what appears to be yours.
Would a freewheel unit permit a fixed turbine engine to be started without also starting the rotors?
In some cases a freewheel unit and a selectable clutch are combined into a single unit. This is the system which I described in my previous post. This sytem is (was) used in Wessex Mk 5, Lynx and SeaKing, and probably may more helicopter types.