Bright guards are making knife (7)
I believe the answer is:
cleaver
'knife' is the definition.
(I know that cleaver is a type of knife)
'bright guards are' is the wordplay.
'bright' becomes 'clever' (bright can mean clever or intelligent).
'guards' indicates putting letters inside (inserted letters are guarded).
'are' becomes 'a' (short for 'are', historical unit of measurement).
'clever' enclosing 'a' is 'CLEAVER'.
'making' acts as a link.
(Other definitions for cleaver that I've seen before include "A clever sort of axe" , "Butcher's knife" , "Meat axe" , "A butcher may use it" , "Butcher's chopper" .)