Reel loops back (5)
I believe the answer is:
spool
'reel' is the definition.
(synonyms)
'loops back' is the wordplay.
'back' is a reversal indicator.
'loops' back-to-front is 'SPOOL'.
(Other definitions for spool that I've seen before include "On which film is wound" , "Loops around a thread holder" , "Loops around with reel" , "Film reel; wind" , "Ribbon holder" .)