Def and First class

Def adjective - Keenly aware of and responsive to the latest developments especially in fashion and entertainment.

First class and def are semantically related In some cases you can use "First class" instead an adjective "Def".

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

Def and first class are semantically related in excellent topic. Sometimes you can use "Def" instead an adjective phrase "First class".