Fairy story and Urban legend

Fairy story noun - A story about fairies; told to amuse children.

Urban legend and fairy story are semantically related. In some cases you can use "Urban legend" instead a noun phrase "Fairy story".

Urban legend noun - A story that appears mysteriously and spreads spontaneously in various forms and is usually false; contains elements of humor or horror and is popularly believed to be true.

Fairy story and urban legend are semantically related. You can use "Fairy story" instead a noun phrase "Urban legend".