cardinal

(noun) (Roman Catholic Church) one of a group of more than 100 prominent bishops in the Sacred College who advise the Pope and elect new Popes.

(noun) the number of elements in a mathematical set; denotes a quantity but not the order. Synonyms: cardinal number.

(noun) a variable color averaging a vivid red. Synonyms: carmine.

(noun) crested thick-billed North American finch having bright red plumage in the male. Synonyms: cardinal grosbeak, Richmondena Cardinalis, Cardinalis cardinalis, redbird.

(adj) serving as an essential component. Synonyms: central, fundamental, key, primal. Examples: "A cardinal rule." "The central cause of the problem." "An example that was fundamental to the argument." "Computers are fundamental to modern industrial structure."

(adj) being or denoting a numerical quantity but not order. Synonyms: cardinal (vs. ordinal). Example: "Cardinal numbers."