Provide closure before old wife ... (5)
I believe the answer is:
endow
'provide' is the definition.
(thesaurus)
'closure before old wife' is the wordplay.
'closure' becomes 'end' (I've seen this before).
'before' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'wife' becomes 'w'.
'end'+'o'+'w'='ENDOW'
(Other definitions for endow that I've seen before include "Provide as a gift" , "Provide with a source of income" , "Set up with money" , "Give permanent income to" , "Pay to found" .)