/ ˈkɑːdɪnl; NAmE ˈkɑːrd-/ noun , adjective
■ noun
1.
a priest of the highest rank in the Roman Catholic Church. Cardinals elect and advise the Pope :
Cardinal Hume
2.
(also ˌcardinal ˈnumber ) a number, such as 1, 2 and 3, used to show quantity rather than order
—compare ordinal
3.
a N American bird. The male cardinal is bright red.
■ adjective
[ only before noun ] ( formal ) most important; having other things based on it :
Respect for life is a cardinal principle of English law.
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WORD ORIGIN
Old English , from Latin cardinalis , from cardo , cardin- hinge. Sense 1 has arisen through the notion of the important function of such priests as “pivots” of church life.