A story of great but unknown age which originally embodied a belief regarding some fact or phenomenon of experience, and in which often the forces of nature and of the soul are personified; an ancient legend of a god, a hero, the origin of a race, etc.; a wonder story of prehistoric origin; a popular fable which is, or has been, received as historical.
A person or thing existing only in imagination, or whose actual existence is not verifiable.
As for Mrs. Primmins's bones, they had been myths these twenty years.