Watch; ensure (3)
I believe the answer is:
see
I believe this clue is a double definition.
'watch' is the first definition.
(I know that watch can be written as see)
'ensure' is the second definition.
(I know that ensure can be written as see)
(Other definitions for see that I've seen before include "Get < court < witness" , "make out" , "Perceive; diocese" , "Observe the papacy in Rome" , "Chelmsford" .)