Stern advocate to retire (4)
I believe the answer is:
back
I believe this clue is a triple definition!
'stern' is the first definition.
(thesaurus)
'advocate' is the second definition.
(thesaurus)
'to retire' is the third definition.
(Other definitions for back that I've seen before include "Support (from behind?)" , "defensive player" , "Golf holes 10-18" , "Rear -- endorse" , "Support - football player" .)