Lament nun's straying and dissolution (9)
I believe the answer is:
annulment
'dissolution' is the definition.
(annulment is a kind of dissolution)
'lament nun's straying' is the wordplay.
'straying' indicates an anagram.
'lament'+'nun'='lamentnun'
'lamentnun' is an anagram of 'ANNULMENT'.
'and' is the link.
(Other definitions for annulment that I've seen before include "Declaration of invalidity, of a marriage say" , "dissolution" , "cancellation" , "recall" , "Invalidation" .)