Promise a victory to old wife (4)
I believe the answer is:
avow
'promise' is the definition.
(I've seen this in another clue)
'a victory to old wife' is the wordplay.
'victory' becomes 'v'.
'to old' becomes 'o' (common abbreviation eg in OE for Old English).
'wife' becomes 'w' (abbreviation).
'a'+'v'+'o'+'w'='AVOW'
(Other definitions for avow that I've seen before include "acknowledge" , "State openly" , "Assert/confess openly" , "Strongly maintain" , "Assert, swear" .)