Feels exceptional to include different (4)
I believe the answer is:
else
'different' is the definition.
(synonyms)
'feels exceptional to include' is the wordplay.
'to include' says the answer is hidden in the clue.
'ELSE' is hidden within 'feels exceptional'.
(Other definitions for else that I've seen before include "Alternatively" , "Besides; different" , "In addition, besides" , "Other than (what is under consideration)" , "In addition; different" .)