Adult in despair about heaven (8)
I believe the answer is:
paradise
'heaven' is the definition.
(paradise is a kind of heaven)
'adult in despair about' is the wordplay.
'adult' becomes 'a'.
'in' is an insertion indicator.
'about' is an anagram indicator.
'despair' anagrammed gives 'pardise'.
'a' placed into 'pardise' is 'PARADISE'.
(Other definitions for paradise that I've seen before include "Elysian fields" , "Idyllic place" , "Heaven; Eden" , "one enjoyed before the fall" , "Scene of bliss" .)