Stern with late deputy (8)
I believe the answer is:
exacting
'stern' is the definition.
(synonyms)
'with late deputy' is the wordplay.
'with' is a charade indicator (letters next to each other).
'late' becomes 'ex'.
'deputy' becomes 'acting' (I've seen this in other clues).
'ex'+'acting' is 'EXACTING'.
(Other definitions for exacting that I've seen before include "Strict, demanding" , "Greatly demanding" , "Requiring hard work and attention" , "Insisting upon" , "Stringent" .)