An Etymological Dictionary of the German Language/Annotated/Pfingsten
Pfingsten, plural, ‘Whitsuntide,’ from Middle High German pfingsten, which in form is really a dative plural (compare Mitternacht), and was used at an early period for all cases; Old High German zi *pfingustin, ‘Whitsuntide,’ is by chance not recorded (Notker uses a pedantic semi-version, zi finfchustin). Formed from Latin and Greek πεντεκοστή (Italian pentecoste, French pentecôte), literally ‘fiftieth day after Easter’; Old Saxon te pincoston, ‘at Whitsuntide,’ Dutch pinksteren, as well as Old Slovenian pętikostij, Whitsuntide.’ While the term Ostern, applied to the Christian passover, was originally a heathen word, which has been retained in English and German, in this instance the ecclesiastical name obtained on the Continent, and that probably prior to the Old High German period, as the initial pf in Middle High German indicates; it was perhaps introduced through a Gothic medium contemporaneously with Kirche and Pfaffe. In English, Whitsunday (Scandinavian hoítadagr) was retained from a very early period, since it was the chief day for baptism, and the newly baptized were wont to wear white garments during that week; hence the German term ‘der weiße Sonntag’. (Dominica in Albis). From quinquagesima, the frequent rendering in Middle Latin of pentecoste, are derived Middle Dutch sinxen, Old Irish cincgigais, ‘Whitsuntide.’