I'm not satisfied with that definition, but then the point of any word is that it stands for a quiddity that cannot be expressed adequately by any other words. There is no such thing as an exact synonym. A myth is a myth is a myth just as a rose is a rose is a rose. Accept no substitutes.
One good thing about it: if the misuse of the word occurs near the beginning of an article- or in a headline- you know you can stop reading right there.