He'll serve people patiently (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.
'serve people patiently' is the wordplay.
'serve' becomes 'wait' (I've seen this in another clue).
'people patiently' becomes 'er' (I am not sure about this - if you are sure you should believe this answer much more).
'wait'+'er'='WAITER'
Can you help me to learn more?
(Other definitions for waiter that I've seen before include "One who serves at table" , "Servant in bar" , "Steward" , "Restaurant staff member" , "One paid to serve" .)