Star, depressed when the day is done? (7)
I believe the answer is:
sundown
'when the day is done?' is the definition.
(I've seen this before)
'star depressed' is the wordplay.
'star' becomes 'sun' (the Sun is a star).
'depressed' becomes 'down' (synonyms).
'sun'+'down'='SUNDOWN'
(Other definitions for sundown that I've seen before include "Event seen in evening" , "Setting time" , "Close of day" , "one time in the evening" , "Sunset" .)