First class and Tops

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

Tops and first class are semantically related. in excellent topic. In some cases you can use "Tops" instead an adjective phrase "First class", when it comes to topics like amazing, most excellent.

Tops adjective - Of the highest quality.

First class and tops are semantically related. You can use "First class" instead an adjective "Tops".