the seventh Sunday after Easter, when Christians celebrate the time when the Holy Spirit came from Heaven to Earth
Origin and usage
The noun Whitsun was first recorded in the 14th century. It is a contraction of ‘Whit Sunday’, a name for the seventh Sunday after Easter that goes back to the earliest days of the English language. Whitsuntide, which generally refers to the period around Whit Sunday, dates from the late 13th century.
Whit Sunday was originally ‘White Sunday’, a reference perhaps to the white robes worn by those who were baptized on that day. Another name for Whitsun is Pentecost, which comes from the Greek word pentēkostē, meaning ‘fiftieth day’. Pentecost refers both to the Christian festival celebrating the descent of the Holy Spirit to Jesus’s disciples and to the Jewish festival of Shavuot, which celebrates the day when God gave the Ten Commandments to Moses. Until 1971 Whit Monday, the day after Whit Sunday, was a movable holiday in the UK. In 1972 it was replaced by the fixed Spring Bank Holiday which always takes place on the last Monday in May, regardless of the date of Easter. In some parts of the UK Whitsuntide was marked by special customs, including parades, fairs and competitions, some of which are still held today.
(Philip Larkin, The Whitsun Weddings)
Easter, Pentecost, Whitsuntide