Cautious passage around river (4)
I believe the answer is:
wary
'cautious' is the definition.
('wary' can be similar in meaning to 'cautious')
'passage around river' is the wordplay.
'passage' becomes 'way' (I've seen this in other clues).
'around' means one lot of letters goes inside another.
'river' becomes 'r'.
'way' going around 'r' is 'WARY'.
(Other definitions for wary that I've seen before include "Careful - cautious" , "Cautious of danger" , "Displaying caution" , "Circumspect" , "Watchful" .)