Wants to be seen turning the key in it (5)
I believe the answer is:
needs
'wants' is the definition.
('need' can be a synonym of 'want')
'seen turning the key in it' is the wordplay.
'turning' says the letters should be written in reverse.
'the key' becomes 'd' (I've seen this in other clues).
'in it' indicates putting letters inside.
'seen' written backwards gives 'nees'.
'nees' placed around 'd' is 'NEEDS'.
'to be' is the link.
(Other definitions for needs that I've seen before include "'..... must when the devil drives'" , "Requires, is in want of" , "Demands" , "Requirements" , "Things that are wanted" .)