ˈkɑː.dɪ.nəl ˈkɑɹdɪnəl ˈkɑː.dɪ.nəl ˈkɑɹdɪnəl ˈsɛntɹəl ˌfʌndəˈmɛntəl ˈpɹaɪməl ˈɹɛdbəːd serving as an essential component a cardinal rule the central cause of the problem an example that was fundamental to the argument computers are fundamental to modern industrial structure crested thick-billed North American finch having bright red plumage in the male being or denoting a numerical quantity but not order cardinal numbers a variable color averaging a vivid red (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