To scowl, it may seem, is a brilliant thing! (6)
I believe the answer is:
glower
'to scowl' is the definition.
(I've seen this in another clue)
'it may seem is a brilliant thing' is the wordplay.
I cannot quite see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
'seem' could be 'glow' (glowing is a kind of seeming) and 'glow' is found in the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for glower that I've seen before include "Look hotly or angrily" , "Stare fiercely" , "Glare" , "Angry stare" , "Angry/sullen look" .)