Downright and First-class

Downright adjective - Being or characterized by direct, brief, and potentially rude speech or manner.

First-class and downright are semantically related. In some cases you can use "First-class" instead an adjective "Downright".

First-class adjective - Of the very best kind.

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