Brief top (5)
I believe the answer is:
prime
This clue is a double definition.
'brief' is the first definition.
(both can mean to inform someone)
'top' is the second definition.
(thesaurus)
(Other definitions for prime that I've seen before include "Main; make usable" , "Of first quality" , "Fundamental - of highest quality" , "Number such as two, three, five, seven, etc" , "Two or three, for example" .)