Talk softly to Sir Simon (7)
I believe the answer is:
prattle
'talk' is the definition.
(I know that prattle is a type of cackle)
'softly to sir simon' is the wordplay.
I cannot quite see how this works, but
'softly' could be 'p' (short for piano, musical term for softly) and 'p' is present in the answer.
The remaining letters 'rattle' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for prattle that I've seen before include "waffle" , "Chatter inanely" , "Idle chatter" , "Talk childishly" , "Talk emptily" .)