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 replace phrase "First class" with "Downright", this terms are similar.

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

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