Sonntag m (genitive Sonntags, plural Sonntage)
From Middle High German sunne(n)tac, sun(n)tac, from Old High German sunnūntag (9th c.), from late Proto-Germanic *sunnōniz dagaz (“day of the sun”), a calque of Latin dies Solis (4th c.). Compare Low German Sünndag, Dutch zondag, West Frisian snein, English Sunday, Danish søndag.