πεντηκοστή

Greek pentēkostḗ (hēmera) meant the fiftieth (day). The word counted days from Passover to the Jewish festival of Shavuot — the harvest festival celebrated fifty days after the first offering of barley. Early Christians mapped their calendar onto the Jewish one: Easter corresponded to Passover, and Pentecost — fifty days after Easter — corresponded to Shavuot. The word is a number. The theology came later.

Acts 2 describes what happened on the fiftieth day: the apostles were gathered together when 'suddenly a sound like the blowing of a violent wind came from heaven,' and 'tongues of fire' appeared over each person, and they began speaking in other languages. The event is considered the birthday of the Christian Church — the moment when the Holy Spirit empowered the apostles to spread the Gospel. The fiftieth day became the most consequential number in Christian history.

Pentecostalism — the Christian movement that emphasizes gifts of the Holy Spirit, especially speaking in tongues — takes its name from this event. The Azusa Street Revival in Los Angeles in 1906 is considered the birth of modern Pentecostalism. Today, Pentecostal and charismatic Christians number over 600 million worldwide, making them the fastest-growing segment of global Christianity. The word Pentecost — a number — names a movement that has reshaped world Christianity.

Whitsunday (White Sunday) is the traditional English name for Pentecost — possibly from the white garments worn by those baptized on the feast. The two names coexist: Pentecost in liturgical and international use, Whitsunday in British tradition. The Greek number and the English color name the same day.