Essayist is to have another boy (7)
I believe the answer is:
addison
'essayist' is the definition.
(Joseph Addison, co-founder of the Spectator)
'is to have another boy' is the wordplay.
I cannot quite understand how this works, but
'is' is present in the answer.
'boy' could be 'don' and 'don' is found within the remaining letters.
The remaining letters 'ad' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
(Other definitions for addison that I've seen before include "Joseph --, co-founder of The Spectator" , "C17-18 English essayist" , "Man of letters" , "Writer of essays" , "author" .)