It goes round and round and back and forth (5)
I believe the answer is:
rotor
I believe this is a double definition.
'it goes round and round' is the first definition.
'back and forth' is the second definition.
'and' acts as a link.
(Other definitions for rotor that I've seen before include "Distributor arm" , "It goes around" , "... and another" , "Turning part of a mechanism" , "Helicopter vane" .)