Supply goal backing Brussels? (5)
I believe the answer is:
endue
'supply' is the definition.
(I've seen this before)
'goal backing brussels?' is the wordplay.
'goal' becomes 'end' (both can mean a purpose).
'backing' is a reversal indicator.
'brussels?' becomes 'EU' (European Parliament is based in Brussels).
'eu' in reverse letter order is 'ue'.
'end'+'ue'='ENDUE'
(Other definitions for endue that I've seen before include "Make investment" , "Supply (with a quality/ability)" , "Invest - supply" , "Provide or imbue" , "Furnish" .)