Eventually leave wife suffering (4)
I believe the answer is:
will
'eventually leave' is the definition.
(to will can mean to leave something in a will)
'wife suffering' is the wordplay.
'wife' becomes 'w'.
'suffering' becomes 'ill'.
'w'+'ill'='WILL'
(Other definitions for will that I've seen before include "Resolve - testament" , "Testament or determination" , "Fixed intention" , "- And Grace, TV series" , "Intend; document" .)