Jack-in-the-box part
I believe the answer is:
lid
'jack-in-the-box part' 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 "Cover for box or eye" , "Covering" , "Cover as for jar" , "Top crust of pie" , "Cap or top for container" .)