Sleep-inducing (9)
I believe the answer is:
soporific
'sleep-inducing' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for soporific that I've seen before include "Sleep-inducing" , "Causing sleepiness" , "making one nod" , "Inducing drowsiness or sleep" , "Inducing mental lethargy" .)