During the papal conclave, a radio journalist asked me the origin of the expression “cardinal error”. I would have liked to tell a colorful tale about an insidious prince of the church who turned the course of history by selecting the wrong pope. Sadly, word origins rarely offer such entertaining stories. In this case, the dictionary says that the adjective cardinal means ‘principal, fundamental, chief, very serious, grave’. The Finnish kardinaali isn’t widely used in a non-ecclesiastical sense; our dictionary mentions cardinal error, cardinal numbers, cardinal bird, and cardinalfish. In English, cardinalappears as an adjective much more often: cardinal principle gets 179 000Google hits, cardinal rule has 688 000 hits, and cardinal direction26 300 000. All cardinals have Latin roots; remaining unaware of thoseorigins could be a cardinal sin.