First class and Prevenient

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

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

Prevenient adjective - In anticipation.

First class and prevenient are semantically related. Sometimes you can use "First class" instead an adjective "Prevenient".