Derisive remark about extremely stout clown (6)
I believe the answer is:
jester
'clown' is the definition.
(jester is a kind of clown)
'derisive remark about extremely stout' is the wordplay.
'derisive remark' becomes 'jeer' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'extremely' suggests removing the centre.
'stout' with its centre removed is 'st'.
'jeer' going around 'st' is 'JESTER'.
Can you help me to learn more?
(Other definitions for jester that I've seen before include "Court humorist" , "Clown employed to entertain a ruler" , "Court joker" , "Funny man, once at court" , "Funny man in olden courts" .)