Slide over top (3)
I believe the answer is:
lid
'top' is the definition.
(I know that lid is a type of top)
'slide over' is the wordplay.
'over' indicates the answer is hidden within the clue (the clue contains or goes 'over' the answer).
'LID' is hidden in the letters of 'slide'.
(Other definitions for lid that I've seen before include "Cover from gliders" , "Top for bottle or eye protector" , "Hat" , "Cap or top for container" , "Top for pot or jar" .)