Myth is Greek mythos, and it wears two Greek markers: the y transliterating upsilon, and the th transliterating theta. The Greek word covered speech, thought, word, discourse, conversation, story and tale — anything delivered by word of mouth. Its own origin is unknown, and one scholar suspects it was borrowed into Greek from an older language of the region.
What is surprising is how recent the English word is. It appears only in 1830, from French mythe and Modern Latin mythus — long after most Greek vocabulary had arrived. English had managed with fable and legend. A useful definition from folklore scholarship: myths are stories about divine beings, revered as true and sacred and tied to religion; once that link breaks and the actors become heroes or giants rather than gods, the story is a folktale rather than a myth.
myth (n.) 1830, from French mythe (1818) and directly from Modern Latin mythus , from Greek mythos "speech, thought, word, discourse, conversation; story, saga, tale, myth, anything delivered by word of mouth," a word of unknown origin. Beekes finds it "quite possibly Pre-Greek." 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, imaginary or fictitious object or individual" is from 1840. also from 1830
myth came in through Greek, and its spelling follows that family's conventions.
How that family writes these sounds
| short /i/ in the middle | y, transliterating υ, where a native word would use imyth, system, syntax, crypt |
What gives it away on the page
| y as a vowel in the middle | Transliterates υ. Native words use i here.myth, system, physics, syntax, crypt |