Sun, perhaps, going down on a day of celebration fast? (6)
I believe the answer is:
starve
'fast?' is the definition.
(to fast is to refrain from eating food)
'sun perhaps going down on a day of celebration' is the wordplay.
I cannot quite see how this works, but
'sun' could be 'star' (I've seen this before) and 'star' is present in the answer.
'day of celebration' could be 've' (VE Day, Victory in Europe Day) and 've' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for starve that I've seen before include "Suffer extreme hunger" , "Suffer from lack of food" , "Go hungry" , "Fail to take in" , "Suffer from food deprivation" .)