cardinal (cardinals plural )
1 n-count; n-title A cardinal is a high-ranking priest in the Catholic church.
In 1448, Nicholas was appointed a cardinal...
2 adj A cardinal rule or quality is the one that is considered to be the most important.
FORMAL
(=chief, principal)
As a salesman, your cardinal rule is to do everything you can to satisfy a customer...
3 n-count A cardinal is a common North American bird. The male has bright red feathers.
cardinal number (cardinal numbers plural )A cardinal number is a number such as 1, 3, or 10 that tells you how many things there are in a group but not what order they are in. Compare ordinal number. n-count
cardinal point (cardinal points plural )The cardinal points are the four main points of the compass, north, south, east, and west. n-count
cardinal sin (cardinal sins plural )If you describe an action as a cardinal sin, you are indicating that some people strongly disapprove of it. n-count
I committed the physician's cardinal sin: I got involved with my patients.