What is the meaning of 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)
• The number of elements in a mathematical set; denotes a quantity but not the order.
  • synonyms: cardinal number
• A variable color averaging a vivid red.
  • synonyms: carmine
• Crested thick-billed North American finch having bright red plumage in the male.
  • synonyms: cardinal grosbeak, Richmondena Cardinalis, Cardinalis cardinalis, redbird

adjective

• Serving as an essential component.
  • usage: "a cardinal rule"; "the central cause of the problem"; "an example that was fundamental to the argument"; "computers are fundamental to modern industrial structure"
  • synonyms: central, fundamental, key, primal
• Being or denoting a numerical quantity but not order.
  • usage: "cardinal numbers"