First class and In good taste

First class noun - Mail that includes letters and postcards and packages sealed against inspection.

In good taste and first class are semantically related. In some cases you can use "In good taste" instead an adjective phrase "First class".

In good taste adjective - Satisfying generally accepted social or esthetic standards.

First class and in good taste are semantically related. Sometimes you can use "First class" instead an adjective phrase "In good taste".