Blue blood and Main line

Blue blood noun - A man or woman of high birth or social position.

Main line and blue blood are semantically related In some cases you can use "Main line" instead a noun phrase "Blue blood".

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

Blue blood and main line are semantically related in society topic. Sometimes you can use "Blue blood" instead a noun phrase "Main line", if it concerns topics such as high-class persons.