First-class and Slightest

First-class adjective - Of the very best kind.

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

Slightest adjective - Being the least in amount, number, or size possible.

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