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Trinity (“the Christian Holy Trinity”) + Sunday
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: The Sunday after Whitsunday/Pentecost in the Western Christian tradition (or the Sunday of Pentecost in the Eastern Christian tradition), observed as a liturgical feast in honor of the Holy Trinity. Full definition →
Trinity (“the Christian Holy Trinity”) + Sunday
Etymology from Wiktionary, CC BY-SA 4.0.