By-and-by and Underworld

By-and-by noun - Time that is to come.

Underworld and by-and-by are semantically related. In some cases you can use "Underworld" instead a noun phrase "By-and-by".

Underworld noun - A social sphere that exists outside of the mainstream.

By-and-by and underworld are semantically related. You can use "By-and-by" instead a noun "Underworld".