First class and Optimum

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

Optimum and first class are semantically related. in most excellent topic. In some cases you can use "Optimum" instead an adjective phrase "First class".

Optimum adjective - Most desirable possible under a restriction expressed or implied.

First class and optimum are semantically related. Sometimes you can use "First class" instead an adjective "Optimum".

Nearby Words: optimal, optimization, optimize, optimise, optimally