Rubbish or a propeller (5)
I believe the answer is:
rotor
'a propeller' is the definition.
(I've seen this before)
'rubbish or' is the wordplay.
'rubbish' becomes 'rot' (both can mean nonsense).
'rot'+'or'='ROTOR'
(Other definitions for rotor that I've seen before include "Bit of chopper" , "Machine part that turns around" , "System of turning helicopter blades" , "Revolving part of a machine, a palindrome" , "Distributor arm" .)