First class and Overlying

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

Overlying and first class are semantically related. in better topic. In some cases you can use "Overlying" instead an adjective phrase "First class".

Overlying adjective - Placed on or over something else.

First class and overlying are semantically related. Sometimes you can use "First class" instead an adjective "Overlying".