Four-star and First class

Four-star adjective - Of the very best kind.

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

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

Four-star and first class are semantically related in eminent topic. Sometimes you can use "Four-star" instead an adjective phrase "First class", if it concerns topics such as high-ranking.