Such aid may be "ebrief' (5)
I believe the answer is:
legal
'such' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for legal that I've seen before include "Sound" , "In accordance with statute" , "It's acceptable" , "In accordance with law" , "Allowed by law" .)