One person of many (3)
I believe the answer is:
man
'one' is the definition.
(thesaurus)
'person of many' is the wordplay.
I cannot really understand how this works, but
'many' could be 'm' (Roman numeral for a thousand) and 'm' is present in the answer.
The remaining letters 'an' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for man that I've seen before include "Vassal; chess piece" , "Attendant" , "Valet" , "Male person" , "See 24" .)