cardinal in WordNet English dictionary

1. crested thick-billed North American finch having bright red plumage in the male
   cardinal  cardinal grosbeak  Richmondena Cardinalis  Cardinalis cardinalis  redbird 
   
2. a variable color averaging a vivid red
   cardinal  carmine 
   
3. (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
   cardinal 
   
4. the number of elements in a mathematical set; denotes a quantity but not the order
   cardinal number  cardinal 
   

1. being or denoting a numerical quantity but not order
   "cardinal numbers"
   cardinal 
   
2. 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"
   cardinal  central  fundamental  key  primal