One person's contribution to many (3)
I believe the answer is:
man
'one' is the definition.
(thesaurus)
'person's contribution to many' is the wordplay.
'person's contribution' becomes 'an' (I can't justify this - if you can you should believe this answer much more).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'many' becomes 'm' (Roman numeral for a thousand).
'an' after 'm' is 'MAN'.
Can you help me to learn more?
(Other definitions for man that I've seen before include "just one" , "Dude" , "race" , "See 24" , "Homo sapiens" .)