Etymology

Possibly from a contraction of þunresdæġ ‎(“Thursday”, literally “Thor's day”), but more likely from Old Norse þōrsdagr or Old Danish þūrsdag ‎(“Thursday”) (compare modern torsdag); all from Proto-Germanic *Þunras dagaz ‎(“Thor's day”), a calque of Latin dies Iovis, equivalent to Old English þunres ‎(“genitive of the god's name Þunor”) +‎ dæġ ‎(“day”). More at thunder, day.