Bric-a-brac mostly running wild (8)
I believe the answer is:
barbaric
'wild' is the definition.
('barbaric' can be a synonym of 'wild')
'bric-a-brac mostly running' is the wordplay.
'mostly' means to remove the last letter.
'running' indicates anagramming the letters.
'bric'+'a'+'brac'='bricabrac'
'bricabrac' with its final letter taken away is 'bricabra'.
'bricabra' with letters rearranged gives 'BARBARIC'.
(Other definitions for barbaric that I've seen before include "Uncivilized" , "Rabbi car for rough and uncivilised" , "Brutal and uncivilised" , "Wild and savage" , "Savage and cruel" .)