Definition of pentecosts:
(n) :
(by extension, Christianity) A festival which falls on the seventh Sunday after Easter which commemorates the event described in Acts 2 of the Bible when the Holy Spirit descended upon the Apostles during the Jewish festival of Pentecost (proper noun, sense 1), conferring on them the miraculous ability to explain the gospel in languages they did not know; also, the Sunday on which the festival is celebrated.
(n) :
(by extension, Christianity) In full day of Pentecost or Pentecost day: the day on which the event commemorated by the festival (proper noun, sense 2) occurred; also, the event itself.
(n) :
(Judaism) Synonym of Shavuot (“a Jewish harvest festival which falls on the sixth day of Sivan in the spring, fifty days after the second day of the Passover when the omer (“sheaf of barley”) is offered; a ceremony held on that day to commemorate the giving of the Torah (“first five books of the Hebrew scriptures”) to Moses and the Israelites on Mount Sinai”).
(n) :
(by extension, Christianity) (by extension) The gift of the Holy Spirit to a Christian; also, the occurrence of this.
(n) :
(by extension, Christianity) Synonym of Whitsuntide (“the week beginning on Whitsunday; also, the weekend which includes Whitsunday”).
(n) :
A surname.