Cardinal

The adjective and noun cardinal (the same word used differently) come from the Latin for 'a hinge' (cardo, genitive cardinis, with an adjective cardinalis). From the idea of 'something on which something turns', the word quickly came to mean 'important': one use at least as old as classical Latin was for the North Pole, the hinge round which the stars turn. From this, the following applications of the word cardinal meaning 'important' have evolved.

• In the Roman Catholic church, the senior clerics, those junior only to the Pope, are called Cardinals. They constitute the 'Sacred College', whose responsibility it is to elect a Pope from among their number on the death of the previous incumbent. There are under 200 of these in the world-wide church.
  • Cardinal red is the colour of a Cardinal's robes; and the North American Cardinal Bird is a species of that colour. The name Cardinal in this sense has also been used for commercial brands, sports teams, and so on.
• In phonetics, the cardinal vowels form the set of agreed standard vowel sounds by reference to which phoneticians can describe any vowel. (The system was proposed by Daniel Jones at the start of the twentieth century, and has stood the test of time.) The intention is to use those sounds formed at the extremes of the oral cavity as points by reference to which any vowel sound can be described.
• Cardinal numbers are those on which counting 'hinges'. They are the 'counting' numbers, 1,2,3,... etc, as opposed to the ordinal numbers, which order things: first, second, third ... etc.
• The cardinal points and winds, etc, in Geography, are North, South, East and West. (It is from this that 'cardinal' sometimes came to mean 'the four most important': those four directions are the easy ones to find (the Pole Star; its opposite; sunrise and sunset).
  • "Cardinal virtues (Lat. virtutes cardinales): in scholastic philosophy, justice, prudence, temperance, and fortitude, accounted the four chief 'natural' virtues as distinguished from the 'theological' virtues of faith, hope, and charity. Some modern writers include these, and speak of 'seven' cardinal virtues; so the 'seven cardinal sins'." (OED).
  • In medieval medicine and into the seventeenth century, the cardinal humours were blood, phlegm, yellow bile, and black bile.
  • You may learn about other such technical terms in your own subjects; or consult works of reference.