Excellent brief (5)
I believe the answer is:
prime
This clue is a double definition.
'excellent' is the first definition.
(thesaurus)
'brief' is the second definition.
(I've seen this before)
(Other definitions for prime that I've seen before include "Brief" , "Best quality, perhaps of beef" , "Fundamental - of highest quality" , "put in the picture" , "hour for prayer" .)