season one of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions; "the regular sequence of the seasons"
whitsun -
Of, or relating to Whitsunday or Whitsuntide.
Wikipedia
Whitsun (Also Whitsunday or Whit Sunday is a festival which originated from the pagan celebration of Summer's Day, the beginning of the Summer half-year, in Europe. In France and England it took on some characteristics of Beltane. Whitsun was later incorporated into Pentecost in the Christian calendar which is the seventh Sunday after Easter and commemorates the descent of the Holy Spirit upon the disciples of Christ.
OmegaWiki Dictionary
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whitsun Feast on the fifthieth day after Passover which commemorates the descent of the Holy Spirit upon the Apostles.