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 adjective - Of the very best kind.

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