In origin this is a Greek word. The word "Mythologia" ("logos" means word) was coined by the philosopher Plato about 400 BC, to describe an imaginative account of events. This was to distinguish such accounts from descriptions which were supposed to be factual (even if based on supernatural events; the difference was more in the approach than the subject matter.) Thus a myth is essentially an imaginative story; it came to suggest a story which, although not believed to be literally true, was recognised as embodying a greater truth. Thus the myth of Oedipus, for example, who in Greek myth l
kills his father and marries his mother, was eventually used in Freudian psychology to illustrate what Freud believed to be a universal truth about the passions and rivalries which are part of every child's development.
In modern times "myth" often has a rather derogatory meaning, as in "urban myth" which implies a rumour spread by credulous people.