n A number indicating quantity, or the size of a set, e.g., one, two, three. (gloss|See w:Cardinal_number|Wikipedia article on Cardinal number.)
a (nautical) Of or relating to the cardinal direction | 'cardinal' directions (north, south, east and west).
a Describing a "natural" number used to indicate quantity (e.g., one, two, three), as opposed to an ordinal number indicating relative position.
n An official in the w:Catholicism | Catholic Church, ranking only below the w:Pope|Pope and the patriarchs. (See w:Cardinal_(Catholicism)|Wikipedia article on Catholic cardinals.)
n Any of various related passerine birds of the family Cardinalidae. (See w:Cardinal_(bird)|Wikipedia article on cardinal birds.)