Nouns

(n)cardinal(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
(n)cardinal number, cardinalthe number of elements in a mathematical set; denotes a quantity but not the order
(n)cardinal, carminea variable color averaging a vivid red
(n)cardinal, cardinal grosbeak, Richmondena cardinalis, Cardinalis cardinalis, redbirdcrested thick-billed North American finch having bright red plumage in the male

Adjectives

(s)cardinal, central, fundamental, key, primalserving 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”
(a)cardinalbeing or denoting a numerical quantity but not order“cardinal numbers”