'Relate' gets adult forward in anguish (9)
I believe the answer is:
appertain
'relate' is the definition.
(thesaurus)
'adult forward in anguish' is the wordplay.
'adult' becomes 'a'.
'forward' becomes 'pert' (I've seen this before).
'in' is an insertion indicator.
'anguish' becomes 'pain' ('pain' can be a synonym of 'anguish').
'pert' put into 'pain' is 'ppertain'.
'a'+'ppertain'='APPERTAIN'
'gets' acts as a link.
(Other definitions for appertain that I've seen before include "Concern" , "Bear on" , "Belong, relate (to)" , "Be relevant to" .)