Revolving part (5)
I believe the answer is:
rotor
'revolving part' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rotor that I've seen before include "Hub with radiating blades" , "Part of, eg, a motor" , "Turning part of machine - a palindrome" , "Revolving blade (as on helicopter)" , "Helicopter supporter" .)