Brief communication raising school rent (7)
I believe the answer is:
notelet
'brief communication' is the definition.
(I've seen this before)
'raising school rent' is the wordplay.
'raising' says the letters should be written backwards.
'school' becomes 'eton' (famous UK public school).
'rent' becomes 'let' (I've seen this in another clue).
'eton' back-to-front is 'note'.
'note'+'let'='NOTELET'
(Other definitions for notelet that I've seen before include "Short annotation or letter" , "means of communication" , "Brief communication" , "Decorative letter" , "Small sheet for letter" .)