Revolving part going left or right (5)
I believe the answer is:
rotor
'revolving part' is the definition.
(I've seen this in another clue)
'going left or right' is the wordplay.
'going left' shows that the letters should be reversed in order (letters written right to left).
'right' becomes 'tor' (I can't explain this - if you can you should give a lot more credence to this answer).
'or' backwards is 'ro'.
'ro'+'tor'='ROTOR'
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "one lifting chopper?" , "Mechanical turning part" , "Turning component" , "Part of, eg, a motor" , "Device to propel a helicopter" .)