Cock and Bull Story
.A corruption of a concocted and bully story. The catch-pennies hawked about the streets are still called cocks—i.e. concocted things. Bully is the Danish bullen (exaggerated), our bull-rush (an exaggerated rush), bull-frog, etc.
Another etymology may be suggested The idol Nergal was the most common idol of the ancient Phœnicians, Indians, and Persians, and Nergal means a dunghill cock. The Egyptian bull is equally notorious under the name of Osiʹris. A cock-and-bull story may therefore mean a myth, in reference to the mythological fables of Nergal and Osiris.
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The French equivalents are faire un coq à lʹâne and un conie de ma mère lʹoie (a mother goose tale).