Having no foundation in fact or probability; incredible because not plausible: applied to idle and absurd rumors and stories. Also cock-and-a-bull.
The Century Dictionary (Public Domain)
Use "cock-and-bull" in a sentence
"No cock-and-bull stories for him, such as you romanticists luxuriate in."
"Donovan cabled Deane in Moscow to tell Fitin one of the biggest cock-and-bull stories one spymaster has ever sent to another spymaster."
"Humorous half-columns in the local papers, written in the customary silly way by unlicked cub reporters just out of grammar school, tickled the fancy of San Francisco for a fleeting moment in that the steamship Mariposa had rescued some sea-waifs possessed of a cock-and-bull story that not even the reporters believed."