Thursday comes from Old English Þūnresdæg, meaning “day of Þunor”—the Anglo-Saxon god of thunder, equivalent to the Norse Thor. The Romans called this day dies Iovis (day of Jupiter), and the Germanic peoples, in their custom, substituted their own sky-god for the Roman one. The result, after a thousand years of linguistic erosion, is Thursday.
Thor is popular again, thanks to Marvel. But popularity in cinema is not a justification for linguistic inefficiency. A student learning English should not need to understand Norse mythology to say “the fourth day of the week.” The cultural reference, however beloved, is irrelevant to the function of the word.
Thursday illustrates a deeper problem with the English week: inconsistency in the root language. Monday and Sunday are celestial bodies (moon, sun). Tuesday through Friday are Germanic gods (Tīw, Wōden, Þunor, Frigg). Saturday is the lone Roman survivor (Saturn). There is no system. There is no pattern. There is just a pile of cultural debris accumulated over 1,500 years.
For the English learner, this means every day-name must be learned individually, as if it were a unique word with no relation to the others—because structurally, it is. Compare this to a numbered week, where learning Week One teaches you the pattern for all six. The cognitive load drops from seven discrete items to one rule applied six times. That is the difference between a well-designed language and a historically inherited one.
Thor can keep his hammer. We will keep our clarity.
Our Recommendation: Week Four. Thunder is for Thor. Numbers are for calendars.