Breathe noisily during sleep (5)
I believe the answer is:
snore
'breathe noisily during sleep' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for snore that I've seen before include "thing which bores" , "Make raucous nasal sound during sleep" , "Breathe noisily during sleep" , "Noise from a sleeper" , "How to keep someone awake while sleeping?" .)