Spread via the Lower Rhineland from Middle Low German dingesdach and Middle Dutch dinsendach (both with variants). Probably from Proto-Germanic *þingsaz-dagaz (“Day of Thingsus”), from *þingsaz + *dagaz. Thingsus is the attested Latin name of a Germanic god who may or may not be the same as Tiw. Further particulars unsettled. Another theory is that it is the “Day of the Thing (“historic Germanic council”)”. Dienstag is cognate with Dutch dinsdag and Luxembourgish Dënschdeg.