Thespian to go off — about to return (5)
I believe the answer is:
actor
'thespian' is the definition.
(synonyms)
'go off about to return' is the wordplay.
'go off' becomes 'rot' (as in food going off).
'about' becomes 'ca' (circa).
'to return' says the letters should be written backwards.
'rot'+'ca'='rotca'
'rotca' back-to-front is 'ACTOR'.
'to' is the link.
(Other definitions for actor that I've seen before include "Luvvy" , "One with role" , "For example, Colman" , "Films/stage worker" , "Stage-player" .)