more reliable (5)
I believe the answer is:
truer
'more reliable' is the definition.
('true' can be similar in meaning to 'reliable')
This is the entire clue.
(Other definitions for truer that I've seen before include "More in accordance with fact" , "That's more like it" , "More relaible" , "More straight and veracious" , "More faithful or straight" .)