Bound by promise in use (7)
I believe the answer is:
engaged
I believe this clue is a double definition.
'bound by promise' is the first definition.
(I've seen this before)
'in use' is the second definition.
(synonyms)
(Other definitions for engaged that I've seen before include "being committed to union" , "Fully occupied" , "prior to one's marriage" , "Promised in marriage" , "Fully committed - to get married?" .)