... and more exceptional solving cases (4)
I believe the answer is:
also
'and' is the definition.
'more exceptional solving cases' is the wordplay.
'cases' indicates the answer is hidden within the clue.
'ALSO' can be found hidden inside 'more exceptional solving'.
(Other definitions for also that I've seen before include "What's more" , "on top" , "Additionally" , "Plus" , "To boot" .)