Appointment in Battle (10)
I believe the answer is:
engagement
I believe this clue is a double definition.
'appointment' is the first definition.
('engagement' can be a synonym of 'appointment')
'battle' is the second definition.
('engagement' can be a synonym of 'battle')
'in' is the link.
(Other definitions for engagement that I've seen before include "get this in the diary?" , "before wedding" , "Agreement to marry" , "Fight" , "Ring maybe to confirm this" .)