A temptation, by the sound of it, to diminish (5)
I believe the answer is:
abate
'diminish' is the definition.
(I know that abate is a more specific form of the action diminish)
'a temptation by the sound of it' is the wordplay.
'temptation' becomes 'bait' (bait is a kind of temptation).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'bait' sounds like 'bate'.
'a'+'bate'='ABATE'
'to' acts as a link.
(Other definitions for abate that I've seen before include "Subside like storm" , "Demolish" , "Subside, grow less" , "Become less strong like storm" , "drop off" .)