A very old wife's state (4)
I believe the answer is:
avow
'state' is the definition.
(thesaurus)
'a very old wife's' is the wordplay.
'a very' becomes 'av' (I've seen this in other clues).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'wife' becomes 'w'.
'av'+'o'+'w'='AVOW'
(Other definitions for avow that I've seen before include "Solemnly declare" , "Solemnly promise" , "Assert - admit" , "Admit openly" , "Affirm, admit" .)