Looked displeased when let down (7)
I believe the answer is:
lowered
'let down' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for lowered that I've seen before include "Moved downwards" , "Let down gently" , "Brought down" , "Moved something down" , "looked sullen" .)