From BiblePortal Wikipedia

Charles Buck Theological Dictionary [1]

A solemn festival of the Christian church, observed on the fiftieth day after Easter, in memory of the descent of the Holy Ghost upon the apostles in the visible appearance of fiery cloven tongues, and of those miraculous powers which were then conferred upon them. It is called Whitsunday or White-Sunday, because this one of that stated times for baptism in the ancient church, those who were baptised put on white garments, as types of that spiritual purity they received in baptism. As the descent of the Holy Ghost upon the apostles happened on that day which the Jews called Pentecost, this festival retained the name of Pentecost among the Christians.

Webster's Dictionary [2]

(1): ( n.) The seventh Sunday, and the fiftieth day, after Easter; a festival of the church in commemoration of the descent of the Holy Spirit on the day of Pentecost; Pentecost; - so called, it is said, because, in the primitive church, those who had been newly baptized appeared at church between Easter and Pentecost in white garments.

(2): ( n.) See the Note under Term, n., 12.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [3]

a festival of the Christian Church commemorative of the descent of the Holy Ghost upon the apostles, as "they were all assembled together with one accord in one place," on the day of Pentecost (q.v.), from which fact the name Pentecost is sometimes used instead of Whitsunday. Blunt says (Dict. of Doct. and list. Theol.), "The etymology of the term has been strangely confused. It has been derived (a) from White Sunday, in supposed allusion to the white garments of the neophytes, as Whitsuntide was one of the two chief seasons for baptism; and (b) from Wytsonday, i.e., Wit, or Wisdom, Sunday, in reference to the outpouring of wisdom upon the apostles. But the real White Sunday is the octave of Easter, or Dominica in albis, and both of these derivations must be abandoned when the proper use of the title is considered. It is not Whit Sunday, but Whitsun Day, as Easter is Easter Day; and the week is Whitsun Week, not Whit Week; and the season Whitsuntide, not Whittide. In Yorkshire, and doubtless also in other parts of England, the feast is commonly called Whissun Day, the accent being strongly thrown on the first syllable; and the two days following, Whissun Monday and Whissun Tuesday. The name is thus derived, as Dr. Neale shows (Essays on Liturgiology, etc.), directly from Pentecost, passing, by various corruptions, Pingsten, Whingsten, into the German Pfingsten and the English Whitsun. The Germans have also their Pfingsten-Woche, in exact correspondence to our Whitsun Week."

Still other derivations of the term are given, Hamon L'Estrange thinking it is derived from the French huit, or eight; because there are eight Sundays between Easter and Pentecost. "Wheatley publishes a letter of the famous Gerard Langbain, written on Whitsuneve, 1650, in reply to a friend who had asked of him the origin of the name, in which it is attempted to be shown that the festival was so called from a custom among our ancestors upon this day to.give all the milk of their ewes and kine to the poor for the love of God, in order to qualify themselves to receive the gift of the Holy Ghost; which milk being then (as it is still in some countries) called white- meat, therefore the day from that custom took its name." It is also suggested that all persons were required to pay their tithe of young before that day or be liable to the wite, or mulct.

Anciently the whole period of fifty days between Easter and Whitsuntide was a sort of festival, and each was observed as a day of joy. We are told that Christians had solemn worship every day, and paid the same respect to these as they did to the Lord's day. All fasting was forbidden, and no one prayed kneeling, the standing posture being considered more in accordance with the joyous spirit of the season, which was the commemoration of our Saviour's resurrection and ascension. At these services the Acts of the Apostles were read, because they contained a history appropriate to the season; alms were freely distributed; slaves were liberated; places of worship were decorated with evergreens; and baptisms were frequently solemnized. At first all persons were baptized as opportunity served; but when the discipline of the Church began to be settled, baptism was confined, except in urgent cases, to Easter and Whitsuntide, including the fifty days' interval.

In countries where Romanism has prevailed, the greatest absurdities have been practiced on this day; fire has been thrown down from elevated places, to represent the cloven tongues of fire; flowers of various hues scattered abroad, in token of the various tongues and gifts of the Spirit; and doves let loose to flutter about the church as an emblem of the Spirit's presence. The following instances are cited from Walcott's Sacred Archaeology (pages 612-613): "At Lichfield, 1197, on Pentecost and the three days ensuing, while the sequence was sung, clouds were by custom scattered." A circular opening still exists in the centre of the vault of Norwich, and there are similar apertures at Exeter. Through it, on Whitsunday, a man, habited as an angel, was let down to cense the rood. At St. Paul's a white dove was let to fly out of it, and a long censer, reaching almost to the floor, was swung from the west door to the choir steps, breathing out over the whole church and company a most pleasant perfume.' At Dunkirk, in 1662, the ceremonial was always performed during the chanting of the Veni Creator, as in Spain. Balsamon alludes to the loosing of the dove in the East. At Orleans, on Whitsunday, during the singing of the prose, birds, lighted tow and resin, wildfire, and flowers were thrown into the cathedral. At St. Julien's, Caen, until the end of the 16th century, seven kinds of flowers were showered down. In Sweden churches are on this festival still decorated with the wind flower and Pentecost lily the daffodil.... In most cathedrals the country folk came in procession on this day, and Sir Thomas More mourns over the unwomanly songs of the women who followed the cross; their offerings then made were called Whitsun-farthings or Pentecostals. On Monday, Tuesday, and Wednesday in Whitsun-week the famous Whitsun plays of Chester were acted from the 14th century until 1594 on Whitsun-Wed-nesday, Whitsonday, the making of the Creed,' being performed. Tilts and tourneys amused knights and fair dames; the morris-dancers delighted the common folks; and in many a rural parish the church ale, a sort of parochial picnic, was kept in an arbor, called Robin-Hood's Bower, followed by dancing, bowls, and archery.... Whitsunday was also called the Easter of Roses.

The Nuttall Encyclopedia [4]

The seventh Sunday after Easter, a festival day of the Church kept in commemoration of the descent of the Holy Ghost.