A system or back to right (5)
I believe the answer is:
rotor
'a system' is the definition.
(I know that rotor is a type of rotating mechanism)
'or back to right' is the wordplay.
'back' shows that the letters should be reversed in order.
'to 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 "Part of electric motor" , "Helicopter lifter" , "US state South of L. Erie" , "Mechanical turning part" , "Revolving dynamic part" .)