Break-up arrangement as part of union deal (6)
I believe the answer is:
prenup
'arrangement as part of union deal' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'break-up' is the wordplay.
'break' becomes 'pren' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pren'+'up'='PRENUP'
Can you help me to learn more?
(Other definitions for prenup that I've seen before include "Financial agreement in case of divorce made by a couple before marriage (abbr)" , "Agreement drawn up before the wedding" , "contract for union" , "Contract between those about to marry" , "Legal agreement before marriage" .)