The rest of the night (5)

I believe the answer is:

sleep

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'the rest' is the definition.
('sleep' can be a synonym of 'rest')

I cannot understand how the rest of the clue works.

(Other definitions for sleep that I've seen before include "Doze, nap" , "crash" , "Natural state of unconscious rest" , "Drop off" , "Snooze" .)

I've seen this clue in the Evening Standard.

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