First-class and Uppermost

First-class adjective - Of the very best kind.

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

Uppermost adjective - Being at a point or level higher than all others.

First-class and uppermost are semantically related. Sometimes you can use "First-class" instead an adjective "Uppermost".