Negative fool with high rank nevertheless (15)
I believe the answer is:
notwithstanding
'nevertheless' is the definition.
(synonyms)
'negative fool with high rank' is the wordplay.
I cannot really see how this works, but
'negative' could be 'not' (I've seen this in another clue) and 'not' is found within the answer.
'with' could be 'and' and 'and' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for notwithstanding that I've seen before include "... in spite" , "Even so" , "Nevertheless" , "anyway" , "Regardless of" .)