Dictionary

One of the officials appointed by the pope in the Roman Catholic Church, ranking only below the pope and the patriarchs, constituting the special college which elects the pope. (See Wikipedia article on Catholic cardinals.)

Any of a genus of songbirds of the finch family, Cardinalis.

Any of various related passerine birds of the family Cardinalidae (See Wikipedia article on cardinals) and other similar birds that were once considered to be related.

(color) A deep red color, somewhat less vivid than scarlet, the traditional colour of a Catholic cardinal's cassock. (same as cardinal red)

Of fundamental importance; crucial, pivotal.

Example: a cardinal rule

Of or relating to the cardinal directions (north, south, east and west).

Example: a cardinal mark

Describing a "natural" number used to indicate quantity (e.g., zero, one, two, three), as opposed to an ordinal number indicating relative position.

Having a bright red color (from the color of a Catholic cardinal's cassock).