Economy class and Second-class

Economy class noun - A class of accommodations on a ship or train or plane that are less expensive than first class accommodations.

Second-class and economy class are semantically related. In some cases you can replace phrase "Second-class" with "Economy class", this phrases are similar.

Second-class adjective - Of little or less value or merit.

Economy class and second-class are semantically related. You can use "Economy class" instead a noun phrase "Second-class".