a.  1.  Of fundamental importance; preëminent; superior; chief; principal.
 
n.  1.  (R. C. Ch.) One of the ecclesiastical princes who constitute the pope's council, or the sacred college.  
2.  A woman's short cloak with a hood. Where's your cardinal! Make haste.  
3.  Mulled red wine.  
4.  the

Noun  1.  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 
2.  cardinal  the number of elements in a mathematical set; denotes a quantity but not the order Synonyms: cardinal number  
3.  cardinal  a variable color averaging a vivid red Synonyms: carmine  
4.  cardinal  crested thickbilled North American finch having bright red plumage in the male  
Adj.  1.  cardinal  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" 
2.  cardinal  being or denoting a numerical quantity but not order; "cardinal numbers" Antonyms: ordinal  being or denoting a numerical order in a series; "ordinal numbers"; "held an ordinal rank of seventh" 
CARDINAL, eccl. law. The title given to one of the highest dignitaries of the court of Rome. Cardinals are next to the pope in dignity; he is elected by them and out of their body. There are cardinal bishops, cardinal priests, and cardinal deacons. See Fleury, Hist. Eccles. liv. xxxv. n. 17, II. n. 19 Thomassin, part ii. liv. i. oh. 53, part iv. liv. i. c. 79, 80 Loiseau, Traite des Ordres, c. 3, n. 31; Andre, Droit Canon, au mot.
Gaussian integer, Grand Penitentiary, Holy Father, Titian, Titianred, abuna, algebraic number, algorismic, algorithmic, aliquot, allabsorbing, antipope, arch, archbishop, archdeacon, archpriest, banner, bishop, bishop coadjutor, bricky, canon, capital, cardinal bishop, cardinal deacon, cardinal number, cardinal priest, carmine, carnation, carnelian, central, cerise, champion, chaplain, cherry, cherrycolored, cherryred, coadjutor, complex number, constitutive, controlling, crimson, crowning, curate, damask, dean, decimal, defective number, differential, digital, diocesan, dominant, ecclesiarch, essential, even, even number, exarch, exponential, ferruginous, fiery, figural, figurate, figurative, finite, finite number, firered, first, flamecolored, flamered, flaming, focal, foremost, fraction, fractional, fundamental, glowing, great, gules, headmost, hegemonic, hierarch, high priest, highest, hot, imaginary, imaginary number, impair, impossible, incarmined, infinite, infinity, inflamed, infrared, integer, integral, ironred, irrational, irrational number, key, lakecolored, laky, lateritious, leading, lobsterred, logarithmic, logometric, lurid, magisterial, main, maroon, master, metropolitan, mixed number, necessary, negative, numeral, numerary, numerative, numeric, odd, ordinal, overriding, overruling, pair, papa, paramount, patriarch, penitentiary, pivotal, polygonal number, pontiff, pope, portwine, positive, possible, prebendary, predominant, preeminent, prelate, premier, preponderant, prevailing, primal, primate, prime number, principal, puce, pure imaginary, radical, ranking, rational, rational number, real, real number, reciprocal, rectangular number, rector, red, reddyed, redlooking, reddened, reddish, reddishamber, reddishbrown, round number, rubicund, rubiginous, rubric, rubricose, ruby, rubycolored, rubyred, ruddied, ruddy, rufescent, rufous, ruling, rural dean, rust, rustred, rusty, scarlet, serial number, sovereign, special, stammel, star, stellar, subdean, submultiple, suffragan, supereminent, supreme, surd, tilered, topflight, topmost, transcendental, transcendental number, transfinite number, uppermost, vermilion, vicar, vinaceous, vital, warm, whole number, wine, winecolored, winered