'Relate' gets adult forward in anguish (9)
I believe the answer is:
Here is my best explanation:
''relate'' is the definition.
'adult forward in anguish' is the subsidiary indication.
'adult' becomes 'a'.
'forward' becomes 'pert' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'anguish' becomes 'pain' ('pain' can be a synonym of 'anguish').
'pert' put into 'pain' is 'ppertain'.
'gets' is the link.
(Other definitions for appertain that I've seen before include "Belong, relate (to)", "Relate (to)", "Concern", "Bear on" and "Be relevant to".)