Jet set and Main line

Jet set noun - A set of rich and fashionable people who travel widely for pleasure.

Main line and jet set are semantically related In some cases you can use "Main line" instead a noun phrase "Jet set".

Main line noun - The principal route of a transportation system.

Jet set and main line are semantically related in society topic. You can use "Jet set" instead a noun phrase "Main line", if it concerns topics such as upper class of people.