All-purpose and First class

All-purpose adjective - Not limited or specialized in application or purpose.

First class and all-purpose are semantically related. In some cases you can use "First class" instead an adjective phrase "All-purpose".

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

All-purpose and first class are semantically related. Sometimes you can use "All-purpose" instead an adjective phrase "First class".