Five-star and First class

Five-star adjective - Of the very best kind.

First class and five-star are semantically related In some cases you can use "First class" instead an adjective phrase "Five-star".

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

Five-star and first class are semantically related in excellent topic. You can use "Five-star" instead an adjective phrase "First class", if it concerns topics such as best, fine, better, top.