(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.