Performed by many a person (4)
I believe the answer is:
done
'performed' is the definition.
(I've seen this before)
'by many a person' is the wordplay.
'by' means one lot of letters go next to another.
'many' becomes 'd'.
'a person' becomes 'one' ().
'd' put next to 'one' is 'DONE'.
(Other definitions for done that I've seen before include "Finished or ended" , "Finished like node" , "This sort of thing is socially acceptable" , "Performed" , "Thoroughly cooked; accomplished" .)