Arranged pre-nup to include nothing advantageous (9)
I believe the answer is:
opportune
'advantageous' is the definition.
('opportune' is associated in meaning with 'advantageous')
'arranged pre-nup to include nothing' is the wordplay.
'arranged' is an anagram indicator.
'include' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'pre'+'nup'+'to'='prenupto'
'prenupto' with letters rearranged gives 'opprtune'.
'opprtune' going around 'o' is 'OPPORTUNE'.
(Other definitions for opportune that I've seen before include "Of time, suitable or favourable" , "Timely, advantageous moment" , "Appropriate" , "in place" , "Occurring at a fitting time" .)