Proved trustworthy (5)
I believe the answer is:
tried
This clue is a double definition.
'proved' is the first definition.
('try' can be a synonym of 'prove')
'trustworthy' is the second definition.
(I've seen this in another clue)
(Other definitions for tried that I've seen before include "Put to the test" , "Sampled" , "Essayed" , "heard in court" , "Tested" .)