An Etymological Dictionary of the German Language/Donnerstag

by Friedrich Kluge

Donnerstag, ‘Thursday,’ from MidHG. donerstac, dunrestac, OHG. donarestag; comp. Du. donderdag, AS. þunresdœg, E. Thursday, OIc. þórsdagr; the day sacred to the OTeut. god þunar (OHG. Donar, OLG. Thunar, OIc. þórr for þōnruz); see Dienstag and Woche. A remarkable form occurs in MidHG. (Bav.), pfinz-tac, ‘Thursday,’ from the equiv. Gr. πέμπτη.