Boring victory paid off (5)
I believe the answer is:
vapid
'boring' is the definition.
(thesaurus)
'victory paid off' is the wordplay.
'victory' becomes 'v'.
'off' is an anagram indicator.
'paid' with letters rearranged gives 'apid'.
'v'+'apid'='VAPID'
(Other definitions for vapid that I've seen before include "Boring, flat" , "Insipid - lacking significance" , "Boring or lifeless" , "Dull, insipid, flat" , "Insipid or uninteresting" .)