Webster's Dictionary 
(1): ( n.) A church festival celebrated on the 6th of January, the twelfth day after Christmas, in commemoration of the visit of the Magi of the East to Bethlehem, to see and worship the child Jesus; or, as others maintain, to commemorate the appearance of the star to the Magi, symbolizing the manifestation of Christ to the Gentles; Twelfthtide.
(2): ( n.) An appearance, or a becoming manifest.
Holman Bible Dictionary 
In much of Eastern Christianity, Epiphany is a celebration of the baptism of Jesus, a recognition of His manifestation to humanity as the Son of God ( Mark 1:9-11 ). In the early centuries, before the observance of Christmas, Epiphany celebrated both the birth of Jesus and His baptism. See Church Year .
Fred A. Grissom
Charles Buck Theological Dictionary 
A Christian festival, otherwise called the manifestation of Christ to the Gentiles, observed on the 6th of January, in honour of the appearance of our Saviour to the three magi, or wise men, who came to adore and bring him presents.
Hastings' Dictionary of the New Testament 
EPIPHANY. —See Calendar, p. 261 f.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
( Ἐπιφάνεια , Τὰ Ἐπιφάνια , the "manifestation" of Christ), one of the oldest festivals of the Christian Church, and mentioned as such by Clement of Alexandria (Stromat. 1:1). Until the time of Chrysostom, it opened in the Eastern Church the cycle of festivals. It denoted at first the baptism of Christ, which, as Chrysostom himself remarks, was, in a higher sense than his birth, his real manifestation to men. A special festival of the birth of Christ arose later than the festival of Epiphany, and up to that time the commemoration of the birth of Christ was included in that of Epiphany. According to the testimony of Clement of Alexandria, it was at first celebrated at Alexandria by the Basilidians, but soon it was introduced into the orthodox Church also. Neander thinks that it did not originate with the Basilidians, but that they derived it from Jewish Christians in Syria and Palestine. The first trace of the festival in the Latin Church is found in 360, when, as Ammianus Marcellinus (21:2) mentions, the emperor Julian took part in a celebration of the festival at Vienne. In the Western Church it came early to denote the manifestation of Christ to the Gentiles, with especial reference to his appearance to the wise men of the East, who came to adore him and bring him presents ( Matthew 2:1-12). Gradually the commemoration of other events in the life of Christ was connected with the celebration of Epiphany, as the working of the first miracle at the wedding at Cana (hence it was called "bethphania," manifestation in a house), and the feeding of five thousand persons (hence the name "phagiphania").
Prominent,.however, in the Latin Church remained the celebration of Epiphany as the manifestation of Christ to the wise men. The tradition of the Church venerated the wise men as the "Three Holy Kings," and the festival itself was commonly called in the Church the festival of the Three Kings (festum trium regum, festum Magorum, festum stellae). Like other high festivals, Epiphany was celebrated by a vigil, by the preaching of homilies, by the reception of the Lord's Supper, and by granting liberty to slaves. During the Middle Ages a dramatic representation of the oblation of the wise men was incorporated into divine worship, and in some countries these performances have maintained themselves until the present century. Peculiar popular amusements also connected themselves with the celebration of the day in Roman Catholic countries, and partly exist even at the present day. In the city of Rome there is on the festival of Epiphany a great exhibition in the College of the Propaganda, young men from all countries making addresses in their native languages, in order thus to represent the appearance of Christ to all nations. In some Western churches, especially in Africa, Epiphany was used as a day of baptism (dies luminum); but Pope Leo I was a decided opponent of this custom, calling it irrationabilem novitatem (an unreasonable novelty). Among the Franks the custom was also known, and Charlemagne mentions it in an epistle to the bishop Garibald, but without approving it. Previously Gregory II, in 726, had forbidden to baptize except on Easter and Pentecost. In the Greek Church it was customary to consecrate the water on this day, and the custom still prevails in Russia. Bingham, Orig. Eccl. book 20, chapter 4; Herzog, Real-Encyklopadie, 4:94; Wetzer u. Welte, Kirchen-Lex. 3:283; Augusti, Handbuch d. christl. Arch.ologie, 1:528; 2:476; Binterim, Denkwiurdigkeiten der christl.-kath. K. volume 5. (See Theophany). (A.J.S.)
The Nuttall Encyclopedia 
As observed in the Christian Church, is a festival held on the 12th day after Christmas, in commemoration of the manifestation of Christ to the Magi of the East; but up to the close of the 4th century the festival also commemorated the incarnation of Christ as well as the divine manifestation at His baptism.