Believable or worthy of belief (8)
I believe the answer is:
credible
This clue is a double definition.
'believable' is the first definition.
(synonyms)
'worthy of belief' is the second definition.
(I've seen this in another clue)
(Other definitions for credible that I've seen before include "Plausible" , "Likely to be believed" , "Convincing" , "Capable of being believed" , "Within the bounds of belief" .)