myth

First recorded in 1820–30; from Late Latin mȳthus, from Greek mŷthos “story, word”

1. See legend.

Myth came into English in the early 19th century via Latin mȳthus “myth, fable” from Greek mŷthos. Latin mȳthus is straightforward: it means “a fable or myth,” such as one would read in Ovid’s Metamorphoses, and in Late Latin, mȳthus is even used as a synonym for fābula “a story, fable.”
Greek mŷthos has a tremendously wide range of meaning: “a word, a speech, mere speech (as opposed to érga ‘deeds’), something said, a thought, an unspoken word, a purpose, a rumor, a report, a saying, fiction (as opposed to lógos ‘historical truth’), the plot of a play, a narrative, a story, a story for children, a fable.”
Sixty percent of Greek vocabulary has no known etymology, and mŷthos is probably within that 60 percent, but it is possible that mŷthos comes from the uncommon Proto-Indo-European root mēudh-, mūdh- (with other variants) “to be concerned with, crave, earnestly desire, think over.” Following this theory, from the variant mūdh-, Greek derives mŷthos and its derivative verb mȳtheîsthai “to speak, converse, tell”; Gothic has maudjan “to remind, remember”; Lithuanian has maûsti “to be concerned with,” and Polish has myśleć “to think.”

C19: via Late Latin from Greek muthos fable, word