Possibly hopes rum will be responsible for sleep (8)
I believe the answer is:
morpheus
'be responsible for sleep' is the definition.
The definition suggests a singular noun which matches the answer.
'possibly hopes rum' is the wordplay.
'possibly' is an anagram indicator.
'hopes'+'rum'='hopesrum'
'hopesrum' is an anagram of 'MORPHEUS'.
'will' is the link.
Can you help me to learn more?
(Other definitions for morpheus that I've seen before include "who controls dreams?" , "Greek god of sleep and dreams" , "In the arms of . . . . . . . . - asleep" , "Roman god of dreams - sleep in his arms" .)