Seen to be highly thought of (8)
I believe the answer is:
regarded
'seen' is the definition.
('regard' can be a synonym of 'see')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for regarded that I've seen before include "Considered or deemed to be" , "Watched" , "Looked at and esteemed" .)