ギリシャ語のmythos(神話)、idea(思想)、story(物語)、myth(神話)、oral tradition(口承伝承)から。擬声語の語源mu(話す)から来ている可能性がある。mythとの語彙の違いを比較してください。
Myths are "stories about divine beings, generally arranged in a coherent system; they are revered as true and sacred; they are endorsed by rulers and priests; and closely linked to religion. Once this link is broken, and the actors in the story are not regarded as gods but as human heroes, giants or fairies, it is no longer a myth but a folktale. Where the central actor is divine but the story is trivial ... the result is religious legend, not myth." [J. Simpson & S. Roud, "Dictionary of English Folklore," Oxford, 2000, p.254]General sense of "untrue story, rumor" is from 1840.