He should have a smart master (5)
I believe the answer is:
valet
'he should have a smart master' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he should have a smart master' is the wordplay.
'he' becomes 'Val'.
'should have' says to put letters next to each other.
'a smart master' becomes 'et' (I can't justify this - if you can you should give a lot more credence to this answer).
'val'+'et'='VALET'
Can you help me to learn more?
(Other definitions for valet that I've seen before include "Gentleman%u2019s gentleman" , "dresser" , "Man's manservant" , "'No man is a hero to his . . . . .'" , "Jeeves?" .)