First class and Second to none

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

Second to none and first class are semantically related. in excellent topic. In some cases you can use "Second to none" instead an adjective phrase "First class", when it comes to topics like most excellent.

First class and second to none are semantically related. Sometimes you can use "First class" instead an adjective phrase "Second to none".