Enlisted person and First class

Enlisted person noun - A serviceman who ranks below a commissioned officer.

First class and enlisted person are semantically related. In some cases you can use "First class" instead a noun phrase "Enlisted person".

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

Enlisted person and first class are semantically related. Sometimes you can use "Enlisted person" instead a noun phrase "First class".