Invent a top missing from videotapes (6)
I believe the answer is:
devise
'invent' is the definition.
('devise' can be a synonym of 'invent')
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for devise that I've seen before include "Formulate or plan" , "Contrive" , "Make (a plan)" , "Formulate or invent" , "Come up with, a plan perhaps" .)