Def and First-rate

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

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

First-rate adjective - Of the very best kind.

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