Sliding cover? (3)
I believe the answer is:
lid
'sliding cover?' is the definition.
'lid' can be an answer for 'cover?' (lid is a kind of cover). I am not sure about the 'sliding' bit.
'sliding cover?' is the wordplay.
'cover?' indicates a hidden word (I've seen 'covering' mean this).
'LID' is hidden in the letters of 'sliding'.
Can you help me to learn more?
(Other definitions for lid that I've seen before include "Hinged or removable cover as for bottle" , "Removable top" , "Pie crust; cover" , "Bottle or jar top" , "Cover for box or eye" .)