Promise from a very old wife (4)
I believe the answer is:
avow
'promise' is the definition.
(I've seen this before)
'a very old wife' 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'
'from' acts as a link.
(Other definitions for avow that I've seen before include "Declare - affirm" , "Assert/confess openly" , "Solemnly declare" , "Assert, swear" , "Asseverate" .)