Acute; strict (6)
I believe the answer is:
severe
This clue is a double definition.
'acute' is the first definition.
(synonyms)
'strict' is the second definition.
(I've seen this before)
(Other definitions for severe that I've seen before include "Extreme - strict" , "Plain, hard" , "Intense; harsh" , "Austere, spartan" , "Arduous - dangerous" .)