Demonstrate brother coming back for saw (7)
I believe the answer is:
proverb
'saw' is the definition.
(a saw can mean a proverb or maxim)
'demonstrate brother coming back' is the wordplay.
'demonstrate' becomes 'prove' (proving is a kind of demonstrating).
'brother' becomes 'br' (abbreviation in titles of monks).
'coming back' says the letters should be written in reverse.
'br' backwards is 'rb'.
'prove'+'rb'='PROVERB'
'for' is the link.
(Other definitions for proverb that I've seen before include "Short saying embodying a supposed truth" , "Short saying expressing a supposed truth" , "encapsulate wisdom" , "Familiar saying" , "Traditional saying" .)