Where does “Trinity Sunday” come from?

Trinity Sunday (English) comes from English Trinity, from Middle English trinite, from Anglo-Norman trinite, from Latin trīnitās, from German Dreieinigkeit, from German Einigkeit, from German -keit, from German -heit.

Trinity Sunday (English): 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

Definitions

  1. 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

Ancestry of “Trinity Sunday”, step by step

Trinity Sunday traces back through two separate lines of ancestry.

via English Trinity

StepLanguageWordMeaning
1EnglishTrinityIn Christian belief, the three persons of the Godhead: the Father, Son and Holy Spirit
2Middle EnglishtriniteA triad; a trinity
3Anglo-Normantrinite
4Latintrīnitāsthreeness; the state of being three
5GermanDreieinigkeitTrinity
6GermanEinigkeitunity; consensus, agreement
7German-keitAlternative form of -heit; -ness, -ty; -ty
8German-heitConverts an adjective into a noun and usually...
9Middle High German-heitness, -ity, -hood; forms nouns from adjectives, denoting the abstract quality of the adjective
10Old High German-heitnature, character
11Proto-West Germanic-haiduhood
12Proto-Germanichaiduzmanner, way; personality, character; appearance
13Proto-Indo-European(s)kayt-

via English sunday

StepLanguageWordMeaning
1EnglishsundayThe first day of the week in many religious traditions, and the seventh day of the week in systems using the ISO 8601 standard; the Christian Sabbath; it follows Saturday and precedes Monday
2Middle EnglishSondaySunday first day of the week
3Old EnglishsunnandægSunday
4Proto-Germanic*Sunnōn dag
5Latindies Solissun's day
6Latinsōl
7Proto-Indo-Europeansóh₂wl̥sun
Every word from Proto-Indo-European (s)kayt-Every word from German -keitEvery word from German -heit