1
general::
An unbelievable tale that is intended to deceive; a tall tale. For example, Jack told us some cock and bull story about getting lost. The origin of this expression is disputed. It may come from a folk tale involving these two animals, or from the name of an English coaching inn where travelers often told such tales. W.S. Gilbert used it in The Yeomen of the Guard (1888), where Jack Point and Wilfred the Jailer make up a story about the hero's fictitious death: ‘‘Tell a tale of cock and bull, Of convincing detail full." [c. 1600]
American Heritage Idioms
2
general::
Phrase(s): cock-and-bull story
a hard-to-believe, made-up story; a story that is a lie. • Don’t give me that cock-and-bull story. • I asked for an explanation, and all I got was your ridiculous cock-and-bull story!
McGrawhill's American Idioms And Phrasal Verbs