Study of wide nature (3)
I believe the answer is:
'study' is the definition.
(term for a study or office)
'of wide nature' is the wordplay.
'of' indicates a hidden word.
'DEN' can be found hidden inside 'wide nature'.
(Other definitions for den that I've seen before include "Gentleman's study or animal's lair" , "Miserable place" , "Wild animal's home" , "Hidden lair of an animal" , "Animal's lair or gent's study" .)