Reversible hub? (5)
I believe the answer is:
This could be a double definition.
'reversible' is the first definition.
'hub?' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "Device to propel a helicopter", "part of chopper", "Arm moving", "Revolver", "Something mechanical".)