... is a bit of a temperamental sort, too (4)
I believe the answer is:
also
'too' is the definition.
(synonyms)
'is a bit of a temperamental sort' is the wordplay.
'is a bit of' says the answer is hidden in the clue.
'ALSO' can be found hidden inside 'temperamental sort'.
(Other definitions for also that I've seen before include "To boot" , "in accompaniment" , "Plus" , "an indication of more to come" , "Item" .)