In use as promised (7)
I believe the answer is:
engaged
I believe this clue is a double definition.
'in use' is the first definition.
('engaged' can be a synonym of 'in use')
'promised' is the second definition.
('engaged' can be a synonym of 'promised')
'as' is the link.
(Other definitions for engaged that I've seen before include "Absorbed" , "Hired; busy" , "Started fighting" , "Occupied with business - about to marry?" , "Affianced" .)