The prospect for the sentinel (7)
I believe the answer is:
lookout
I believe this clue is a double definition.
'the prospect' is the first definition.
(thesaurus)
'the sentinel' is the second definition.
('lookout' can be a synonym of 'sentinel')
'for' is the link.
(Other definitions for lookout that I've seen before include "Person on watch for dangers" , "View" , "One who keeps watch, a sentry" , "Observer; concern" , "Observer, sentinel" .)