First class and Leonine

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

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

Leonine adjective - Of or characteristic of or resembling a lion.

First class and leonine are semantically related. Sometimes you can use "First class" instead an adjective "Leonine".