Paper (5)
'paper' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for essay that I've seen before include "Analytic or interpretive literary composition (5_" , "Try; dissertation" , "Old experiment" , "Endeavour" , "Written academic work" .)
(Other definitions for moon that I've seen before include "show a lot of cheek" , "Expose one's buttocks" , "down one's pants" , "Remove boxers, maybe" , "crescent perhaps" .)