Unlikely I felt that this might be wicked (6)
I believe the answer is:
tallow
'this might be wicked' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'unlikely i felt that' is the wordplay.
'unlikely' becomes 'tall' (as in a tall tale).
'i felt that' becomes 'ow' ('ow' is an expression of pain).
'tall'+'ow'='TALLOW'
Can you help me to learn more?
(Other definitions for tallow that I've seen before include "Animal oil used in making soap and candles" , "Candle ingredient" , "Melted, clarified animal fat" , "Fat used in candles/soaps" , "Contributor to soap" .)