Pentecost vs. Whitsun — What's the Difference?

The Christian holiday of Pentecost is celebrated on the 50th day (the seventh Sunday) from Easter Sunday. It commemorates the descent of the Holy Spirit upon the Apostles and other followers of Jesus Christ while they were in Jerusalem celebrating the Feast of Weeks, as described in the Acts of the Apostles (Acts 2:1–31).

Whitsun (also Whitsunday or Whit Sunday) is the name used in Britain, and throughout the world among Catholics, Anglicans and Methodists, for the Christian High Holy Day of Pentecost. It is the seventh Sunday after Easter, which commemorates the descent of the Holy Spirit upon Christ's disciples (as described in Acts 2).

(Christianity) The seventh Sunday after Easter, commemorating the descent of the Holy Spirit upon the disciples. Also called Whitsunday.

Of, relating to, or observed on Whitsunday or at Whitsuntide.

(Judaism) See Shavuot.

Of, pertaining to, or observed at, Whitsuntide; as, Whitsun week; Whitsun Tuesday; Whitsun pastorals.

A solemn festival of the Jews; - so called because celebrated on the fiftieth day (seven weeks) after the second day of the Passover (which fell on the sixteenth of the Jewish month Nisan); - hence called, also, the Feast of Weeks. At this festival an offering of the first fruits of the harvest was made. By the Jews it was generally regarded as commemorative of the gift of the law on the fiftieth day after the departure from Egypt.

Christian holiday; the week beginning on Whitsunday (especially the first 3 days)

A festival of the Roman Catholic and other churches in commemoration of the descent of the Holy Spirit on the apostles; which occurred on the day of Pentecost; - called also Whitsunday.

Seventh Sunday after Easter; commemorates the emanation of the Holy Spirit to the apostles; a quarter day in Scotland

(Judaism) Jewish holy day celebrated on the sixth of Sivan to celebrate Moses receiving the Ten Commandments