The quality of being able to be believed or convincing; credibility.
From believe + -able + -ity (suffix creating abstract nouns of quality). Follows the pattern of adding -able to create an adjective, then -ity to nominalize it into a quality descriptor.
A magician's believability is a carefully constructed illusion—the better the trick, the higher the believability, which is why we're fascinated by being fooled in controlled ways!
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