Webster's Dictionary 
(1): (a.) Mulled red wine.
(2): (a.) One of the ecclesiastical princes who constitute the pope's council, or the sacred college.
(3): (a.) Of fundamental importance; preeminent; superior; chief; principal.
(4): (a.) A woman's short cloak with a hood.
Charles Buck Theological Dictionary 
One of the chief governors of the Romish church, by whom the pope is elected out of their own number, which contains six bishops, fifty priests, and fourteen deacons: these constitute the sacred college, and are chosen by the pope.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
(cardinalis, principal; from cardo, a hinge), the title of an eminent class of dignitaries in the Roman Church, so styled as if the axle or hinge on which the whole government of the Church turns; or as they have, from the pope's grant, the hinge and government of the Romish Church. Pope Eugenius IV states the derivation from cardo, a hinge, as follows: Sicut per cardinem volvitur ostium domes, ita super hos Sedes Apostolica, totius Ecclesice ostium, quiescit et sustentatur (see Dufresne, s.v. cardinalis).
1. Cardinal Priests, Etc. — In early days the name cardinal was used with great latitude in the Roman Church. Its first definite application was to the principal priests of the parishes of Rome; the chief priest of a parish, next to a bishop, being presbyter Cardinalis, to distinguish him from the other priests who had no church. It is uncertain when the term was first applied, but it seems that Stephen IV (770) was the first who selected seven bishops out of the number of the see of Rome, and gave them the title of cardinal, obliging them to say mass every Sunday in St. Peter's. Leo IV, in a council of Rome held in 853, calls them Presbyteros Sui Cardinis, and their churches parochas cardinales. At a subsequent period the priests and deacons of other cities of importance assumed the title of cardinal, to distinguish them from other priests and deacons over whom they claimed supremacy; but the popes subsequently ordained that none but those whom they had chosen should be honored with that title. Among those whom the popes thus appointed were the seven bishops suburbicarii, who took their titles from places in the neighborhood of Rome. These bishops were called hebdomadarii, because they attended the pope for a week each in his turn. These cardinals took part with the Roman clergy in the election of the pope, who was generally chosen from their number. But it was not until the edict of Nicolas II, A.D. 1059 (see below), that the body of cardinals, as such, had a proper existence as a recognized branch of the ecclesiastical system.
2. College Of Cardinals. — "The college of Cardinals, in its origin, was nothing else than the council which, according to the canons, every metropolitan was obliged to consult, and in which, during a vacancy, all the metropolitan powers resided, viz., the synod of provincial bishops, and the chapter of the metropolitan church; and it is not difficult to see that this college would share in the supreme glory of the see of Rome, in the same proportion as every other church participated in the honor of its particular metropolitan. It was not, however, for a long time that the cardinalate attained to its present excessive and usurped degree of power and dignity. In the Synod of Rome, under Benedict VIII, in 1015, the cardinals, priests, and deacons still signed after the bishops, and the cardinalbishops after other bishops of older standing in the order than themselves; but in 1050 we find a vast change, for Humbertus, bishop of Silva Candida, who was a cardinal-bishop of the see of Rome, took precedence at Constantinople of the archbishop of Amalfi; and from that time we perceive the cardinal- bishops, and soon even the priests and deacons, arrogating to themselves that precedence over all other ecclesiastical dignitaries which they now possess. This, however, was not done without resistance. Thus, in 1440, the archbishop of Canterbury refused to allow to the cardinal-archbishop of York the precedence which he claimed; whereupon Pope Eugenius IV wrote to the former, reprehending him for his conduct, and declaring that the cardinalate had been instituted by St. Peter himself, and that the dignity of the cardinals, who, with the pope, governed the Universal Church, and sat in judgment upon bishops, was, past all doubt, greater than that of even patriarchs, who had jurisdiction over only a part of the Church, and from whom there lay an appeal to the see of Rome. The same dispute occurred between the cardinal-bishop of Cracow and the primate of Gnesna in 1449. As time went on, these arrogant pretensions of the college increased: we find the cardinals saying to Pope Pius, Cardinales pares Regibus haberi; so the cardinal of Pavia, in several places, Cardinalem . . . cujus dignitas antefertur Regibus. In 1561 the cardinals of Lorraine and Guise refused to give precedence to the princes of the blood royal. To such an excess had this arrogance and grasping at dignity attained in the sixteenth century, that the bishops at the Council of Lateran, under Leo X, in 1512, came to the resolution either to keep away altogether, or to negative every proposition, until their grievances were redressed.
"The Council of Rome, under Nicolas II, 1059, grants to the college of Cardinals, or rather (Song of Solomon 1) to the cardinal-bishops, the principal voice in the election of the pope; and, according to Peter Damianus, the election of a pope contrary to the opinion of the cardinal-bishops was null. Pandulphus remarks, with regard to the election of Gelasius II, that although all the cardinals, clergy, and people had a voice in the election, the cardinal- bishops alone had the right of approving or disapproving the election, and consecrating the elect. None but cardinals are now eligible to the papacy. Pius IV seems to have been the first who restricted the election to the cardinals only" (Landon, Eccl. Dictionary, s.v.).
3. Number Of Cardinals. — In 1331 there were twenty, and after the death of Clement VI, in 1352, the cardinals resolved that that number should not be exceeded. In 1378, at the election of Urban VI, there were twenty- three. The Council of Basle fixed the number at twenty-four, and the college itself appears to have been all along very jealous of an increase to ts numbers. However, Leo X set the example of a large increase, creating in one day thirty-one new cardinals, in order to neutralize the opposition made to him by a cardinal who had formed a party in the college. The bull Compacti, in 1555, fixed the number at forty, and forbade to create more. But the college has since been enlarged to seventy members, the number at which it was finally fixed by the bull of Pope Sixtus V in 1586: six of these are bishops, fifty priests, and fourteen deacons. The number of cardinal- bishops was at first seven, but it was shortly afterward altered to six, at which it has ever since remained. These bishops, on Sundays and festivals, officiate as the pope's vicars at the altar of St. Savior, in the church of Lateran, or assist the pontiff when he officiates in person. The cardinal- bishops in 1867 were Mario Mattei, bishop of Ostia and Velletri, July 2, 1832; Constantino Patrizi, bishop of Porto and St. Rufina, June 23, 1834; Luigi Amat, bishop of Palestrina, May 19, 1837; Anthony Cagiano de Azevedo, bishop of Frascati, Jan. 22, 1844; Girolamo d'Andrea, March 15, 1852; Ludovico Alfieri, bishop of Alhano, April 21, 1845. A list of the cardinal-priests and cardinal-deacons is given in the Almanac de Gotha and in the Roman Catholic almanacs annually.
4. Costume. — The dress of a cardinal is a red soutane, a rochet, a short purple mantle, and a red hat. The cardinals began to wear the red hat at the Council of Lyons in 1245: the privilege was granted by Pope Innocent IV. Its color is designed to show that the cardinals are bound to shed their blood in the cause of the Church, if need be. A number of symbolical ceremonies accompany the investiture. The hat is given by the pope's own hands; and many cardinals who do not visit Rome die without ever having received it. The only exception is in favor of members of royal houses, to whom the hat is sent. As the cardinals, when dressed in the sacred vestments, could not wear the red hat, and had therefore no other distinction to mark the difference between them and prelates of an inferior rank except their place, Paul II permitted them to wear the red bonnet (Rubrum Capitium), which previously had been the prerogative of the pontiff alone. They were also permitted the red habit by the same pope.
5. The Style of the cardinals, until the time of urban VIII, was Most Illustrious; that pope, however, Jan. 10, 1630, granted to all the cardinals the title of Eminence. The cardinal-bishops are titled Eminentis-Simi. A carriage and livery servants are obligatory parts of the establishment of a cardinal.
6. Form Of Making Cardinals. — The pope alone can elevate any one to the cardinalate, which he does by declaring in the secret Consistory the names of those whom he proposes to make cardinals, saying Habemus Fratres. He afterward, in a public Consistory, puts the red bonnet on the head of the newly-appointed cardinal, signs him with the cross, and creates him cardinal, with the form of words following: Ad Laudem Omnipotentis Dei Et Sanctae Sedis Apostolicae Ornamentumn Accipe Galerumn Rubrum, Insigne Singularis Dignitai'S Cardinalatus, Per Quod Designatur, Quod Usque Ad Mortem Et Sanguinis Ejfusionem Inclusive, Pro Exaltatione Sanctae Fdei, Pace Et Quietate Populi Christiani, Augmento Et Statu Sacrosanctae Romanae Ecclesice To Intrepidum Eahibere Debeas. In Nomine Patris t, Et Filii T, Et Spiritus Sancti t, Amen.
7. Duties, Privileges, Etc., Of Cardinals. — The legal Status of cardinals, and their relations to the papal see, are fixed by the Ceremoniale Romanum, by the decrees of Trent (Sess. 24, Cap. 1, De Reform.), by the bull of Sixtus V, Religiosa Sanct., April 13, 1587, and by later papal constitutions. By the canon of Trent, as above cited, it is decreed "that all and each of the particulars which have been elsewhere ordained, in the same synod, touching the life, age, learning, and other qualifications of those who are to be promoted to be bishops, the same are also to be required in the creation of cardinals of the holy Roman Church, even though they be deacons; whom the most holy Roman pontiff shall, as far as can conveniently be done, choose out of all the nations of Christendom, as he shall find persons competent. Finally, the same holy synod, moved by the so many most grievous difficulties of the Church, cannot avoid calling to mind that nothing is more necessary for the Church of God than that the most blessed Roman pontiff apply especially here that solicitude which, by the duty of his office, he owes to the universal Church, that he take unto himself, to wit as cardinals, men the most select only." No bastard, nor ecclesiastic who has not been a year in orders, can be chosen. Cardinals may be taken from any country, but the pope has always chosen a large majority of Italians. In October, 1866, of 59 cardinals, 39 were Italians by birth, 8 Frenchmen, 4 Spaniards, 4 Germans, 1 Croatian, 1 Belgian, 1 Portuguese, and 1 Irishman. The rank of cardinal is next to that of pope, and the pope is always chosen from their number. Since the time of Alexander III the right of electing the pope lies in the College of Cardinals. (See Pope). The pope often employs cardinals as ambassadors, and the individual thus employed is styled Legate A Latere. A cardinal-legate acted, before the recent absorption of the Papal States by the kingdom of Italy, as governor of the northern provinces of the Papal States, which thence received the name of legations. The chief secretary of state, the Camerlengo, or minister of finances, the vicar of Rome, and other leading officials, are always chosen from among the cardinals. Their dignity is held to place them in the rank of European princes; and, so long as the temporal power of the popes lasted, they held civil as well as ecclesiastical offices. For the Congregations, i.e. papal commissions, which are under the direction of cardinals, (See Papal Congregation).
8. Literature. — Ferraris, Promta Bibliotheca, 2:99; Kleiner, De Orig. Et Antiq. etc. Cardinalium; Buddeus, De Orig. Card. Dignitatis (Jena, 1695, 4to); Bez, De, Orig. et Antiq. Cardinalium (Heidelberg, 1767, 4to); History of the Cardinals, to Pope Clement IX, from the Italian (Lond. 1670, fol.); Augusti, Denkw Ü rdig. p. 151; I Thomassin, Vet. et Nov. ecclesiae Discplina (vol. 1, 100:113); Siegel, Handbuch der Alterth Ü mer, 1:329; Coleman, Christian Antiquities, ch. 3, § 6; Herzog, Real- Encyklop Ä die, 2:577. (See Congregation); (See Curia); (See Pope).