Faithful, dependable (6)
I believe the answer is:
trusty
I believe this clue is a double definition.
'faithful' is the first definition.
(similar in meaning)
'dependable' is the second definition.
(associated in meaning)
(Other definitions for trusty that I've seen before include "Reliable, honest and firm" , "Reliable, faithful" , "Reliable (prisoner)" , "Devoted" , "Reliable, well-behaved prisoners with privileges" .)