First class and Whilom

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

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

Whilom adjective - Having been such at some previous time.

First class and whilom are semantically related. Sometimes you can use "First class" instead an adjective "Whilom".