One unlikely to be out for whole night (9)
I believe the answer is:
insomniac
'night' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for insomniac that I've seen before include "One lying awake" , "who won't get off?" , "Can't drop off" , "One who can't sleep" , "This person can't sleep" .)