Not a man of substance presumably (6)
I believe the answer is:
nobody
'not a man of substance presumably' is the definition.
I can't judge whether this defines the answer.
'not a man of substance' is the wordplay.
I cannot really understand how this works, but
'not' could be 'no' (negative) and 'no' is located in the answer.
'man' could be 'ody' and 'ody' is found in the answer.
'substance' could be 'b' (B is an example) and 'b' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for nobody that I've seen before include "Eg Pooter" , "problem for Morse?" , "Literary diarist" , "being without value" , "Unimportant person" .)