Declare a victory over wife (4)
I believe the answer is:
avow
'declare' is the definition.
(I know that avow is a kind of declare)
'a victory over wife' is the wordplay.
'victory' becomes 'v'.
'over' shows that the letters should be reversed in order.
'wife' becomes 'wo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'wo' reversed gives 'ow'.
'a'+'v'+'ow'='AVOW'
Can you help me to learn more?
(Other definitions for avow that I've seen before include "acknowledge" , "Assert or confess openly" , "Affirm, admit" , "Assert/confess openly" , "Solemnly promise" .)