Wicked sin in Adonis (8)
I believe the answer is:
devilish
'wicked' is the definition.
(similar in meaning)
'sin in adonis' is the wordplay.
'sin' becomes 'evil' (I've seen this in another clue).
'in' means one lot of letters goes inside another.
'adonis' becomes 'dish' (I can't explain this - if you can you should give a lot more credence to this answer).
'evil' going inside 'dish' is 'DEVILISH'.
Can you help me to learn more?
(Other definitions for devilish that I've seen before include "naughty" , "Very wicked" , "like Screwtape" , "Mischievous; rakish" , "Diabolical" .)