Sorry to natter stupidly about writer (9)
I believe the answer is:
repentant
'sorry' is the definition.
(similar in meaning)
'natter stupidly about writer' is the wordplay.
'stupidly' indicates anagramming the letters (a stupid ordering of the letters).
'about' means one lot of letters goes inside another.
'writer' becomes 'pen' (something which writes).
'natter' anagrammed gives 'retant'.
'retant' going around 'pen' is 'REPENTANT'.
'to' acts as a link.
(Other definitions for repentant that I've seen before include "showing contrition" , "Feeling remorse for misdeeds" , "Contrite" , "Regretful" , "sorry state" .)