He'll bring drink one assumes (6)
I believe the answer is:
waiter
'he'll' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'drink one assumes' is the wordplay.
I cannot quite understand how this works, but
'drink' could be 'it' and 'it' is found within the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'bring' is the link.
Can you help me to learn more?
(Other definitions for waiter that I've seen before include "Server in restaurant" , "Restaurant staff member" , "Table server" , "Servant in bar" , "Herr Ober (Ger.)" .)