What is Cardinal ?
Cardinal is (adj) very important Her attendance at the meeting is of cardinal importance.(noun) 1. one of the most important priests in the Catholic church, after the Pope The cardinals meet in Rome to elect the Pope. Cardinal Lamont has written an article in today’s paper. (NOTE: also used as a title before a surname: Cardinal Wolsey) 2. a bright red bird, which comes from the southern USA
source: Easier English, Student Dictionary Upper Intermediate Level