Over 501 (4)
I believe the answer is:
done
'over' is the definition.
(both can mean finished)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for done that I've seen before include "Concluded (and dusted?)" , "Finished like node" , "Thoroughly cooked; accomplished" , "Finished or ended" , "Artist's workroom" .)