Inferior, so it could be better (5)
I believe the answer is:
under
'inferior' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for under that I've seen before include "See 7" , "Sub" , "Governed by" , "Beneath or subordinate to" , "Inferior" .)