1. believe- to think that something is true, correct or real:
Strangely, no one believed us when we told them we’d been visited by a creature from Mars.
[+ that] He believes that all children are born with equal intelligence.
[+ speech] She’s arriving tomorrow, I believe.
“Is she coming alone?” “We believe not/so (= We think she is not/is).”
[+ object + to infinitive] I believe her to be the finest violinist in the world.
[+ object + adjective] All the crew are missing, believed dead.

believable ]
adjective
If something is believable, it seems possible, real or true:
I didn’t find any of the characters in the film believable.

believer ]
noun [C]
a person who has a religious belief or has confidence in the benefit of something:
She’s been a believer since she survived a terrible car accident.
Harvey’s a great believer in health food.
I’m a great believer in allowing people to make their own mistakes.