Jar top (3)
I believe the answer is:
lid
'jar top' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lid that I've seen before include "Bottle or jar top" , "Hinged or removable cover as for bottle" , "Covering" , "Top for bottle or eye protector" , "Removable cover of a container" .)