adjective Of fundamental importance; crucial, pivotal.
a cardinal rule
adjective Of or relating to the cardinal directions (north, south, east and west).
a cardinal mark
adjective Used to describe quantity (e.g., zero, one, two, three), as opposed to an ordinal number indicating relative position. (See Cardinal_number.)
adjective Having a bright red color (from the color of a Catholic cardinal’s cassock).
adjective Being one of the signs Aries, Cancer, Libra and Capricorn, associated with initiation, creation, and force.
noun One of the officials appointed by the pope in the Roman Catholic Church, ranking only below the pope, equal to the patriarchs, constituting the special college which elects the pope.
noun Any of various species of New-World passerine songbird in the genus Cardinalis, or in the family Cardinalidae more generally, or of similar appearance and once considered to be related to the former; so called because of their red plumage. (See Wikipedia article for taxonomical information.)
noun A deep red color, somewhat less vivid than scarlet, the traditional colour of a Catholic cardinal's cassock.