Make sure you understand (3)
I believe the answer is:
see
I believe this clue is a double definition.
'make sure' is the first definition.
(synonyms)
'understand' is the second definition.
(I know that see is a kind of the understand)
'you' acts as a link.
(Other definitions for see that I've seen before include "Bishops office" , "Observe the bishop's domain" , "Experience" , "Realize" , "Bishop's seat" .)