Former wife in St. Helier, somehow (9)
I believe the answer is:
erstwhile
'former' is the definition.
(synonyms)
'wife in st helier somehow' is the wordplay.
'wife' becomes 'w'.
'in' is an insertion indicator.
'somehow' indicates anagramming the letters.
'st'+'helier'='sthelier'
'sthelier' with letters rearranged gives 'ersthile'.
'w' going into 'ersthile' is 'ERSTWHILE'.
(Other definitions for erstwhile that I've seen before include "Former, previous" , "Quondam" , "Former - list where (anag)" , "Formerly" , "In the past" .)