First-class and Upper-class

First-class adjective - Of the very best kind.

Upper-class and first-class are semantically related In some cases you can use "Upper-class" instead an adjective phrase "First-class".

Upper-class adjective - Of high birth, rank, or station.

First-class and upper-class are semantically related in eminent topic. Sometimes you can use "First-class" instead an adjective phrase "Upper-class", if it concerns topics such as high-ranking.