It turns backwards and forwards (5)
I believe the answer is:
rotor
'it turns' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rotor that I've seen before include "Eddy" , "Mechanical turning part" , "Chopper blade" , "Turning component" , "Machine part that turns around" .)