WHITSUN-DAY, or WHITSUNDAY. The derivation of the name is doubtful; some taking it from Whitsun, a corruption of Pentecosten, the old Anglo-Saxon name for the day; and some from White Sunday, because those who had been baptized on its eve wore white robes. This festival is the birthday of the Church, and has been observed, like Easter, from the first days of Christianity. (See Pentecost.)