Jack, the boy possibly with Samuel (7)
I believe the answer is:
johnson
'with samuel' is the definition.
The definition suggests a singular noun which matches the answer.
'jack the boy' is the wordplay.
'jack' becomes 'john' (I can't explain this - if you can you should give a lot more credence to this answer).
'the boy' becomes 'son' ('son' can be a synonym of 'boy').
'john'+'son'='JOHNSON'
'possibly' acts as a link.
Can you help me to learn more?
(Other definitions for johnson that I've seen before include "one of two presidents" , "Lexicographical doctor" , "harmless drudge?" , "Samuel -, lexicographer" , "Lexicographic doctor" .)