Understands; watches (4)
I believe the answer is:
sees
I believe this is a double definition.
'understands' is the first definition.
('see' can be a synonym of 'understand')
'watches' is the second definition.
(I know this)
(Other definitions for sees that I've seen before include "Bishoprics" , "Notices" , "Looks (both ways!)" , "Clocks" , "Observes or perceives" .)