myth

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A traditional, typically ancient story dealing with supernatural beings, ancestors, or heroes that serves as a fundamental type in the worldview of a people, as by explaining aspects of the natural world or delineating the psychology, customs, or ideals of society.
• noun Such stories considered as a group.
• noun A popular belief or story that has become associated with a person, institution, or occurrence, especially one considered to illustrate a cultural ideal.
• noun A fiction or half-truth, especially one that forms part of an ideology.
• noun A fictitious story, person, or thing.

from The Century Dictionary.

• noun A traditional story in which the operations of natural forces and occurrences in human history are represented as the actions of individual living beings, especially of men, or of imaginary extra-human beings acting like men; a tale handed down from primitive times, and in form historical, but in reality involving elements of early religious views, as respecting the origin of things, the powers of nature and their workings, the rise of institutions, the history of races and communities, and the like; a legend of cosmogony, of gods and heroes, and of animals possessing wondrous gifts.
• noun In a looser sense, an invented story; something purely fabulous or having no existence in fact; an imaginary or fictitious individual or object: as, his wealthy relative was a mere myth; his having gone to Paris is a myth. Myth is thus often used as a euphemism for falsehood or lie.
• noun A landmark for directing the course of a vessel through a channel, or along a dangerous shore.
• noun An abbreviation of mythological, mythology.

from the GNU version of the Collaborative International Dictionary of English.

• noun A story of great but unknown age which originally embodied a belief regarding some fact or phenomenon of experience, and in which often the forces of nature and of the soul are personified; an ancient legend of a god, a hero, the origin of a race, etc.; a wonder story of prehistoric origin; a popular fable which is, or has been, received as historical.
• noun A person or thing existing only in imagination, or whose actual existence is not verifiable.
• noun history made of, or mixed with, myths.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A traditional story which embodies a belief regarding some fact or phenomenon of experience, and in which often the forces of nature and of the soul are personified; a sacred narrative regarding a god, a hero, the origin of the world or of a people, etc.
• noun uncountable such stories as a genre
• noun A commonly-held but false belief, a common misconception; a fictitious or imaginary person or thing; a popular conception about a real person or event which exaggerates or idealizes reality.
• noun A person or thing held in excessive or quasi-religious awe or admiration based on popular legend

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a traditional story accepted as history; serves to explain the world view of a people