Trinket not quite so unappealing (9)
I believe the answer is:
charmless
'quite so unappealing' is the definition.
I can't tell whether this defines the answer.
'trinket not' is the wordplay.
'trinket' becomes 'charm' (I can't explain this - if you can you should give a lot more credence to this answer).
'not' becomes 'less' (I've seen this in other clues).
'charm'+'less'='CHARMLESS'
Can you help me to learn more?
(Other definitions for charmless that I've seen before include "Unattractive" , "not winning" , "Lacking any appeal" , "Without attractive features" .)