Time for another day of the week!
In most languages, Thursday is the day of thunder. As usual, we can thank the Romans for this. They started with the day for their thunder god, Jupiter (or in Greek terms, Zeus). Actually, if you want to get technical, it’s a reference to Jove, better known as Jupiter (it means Father Jove, referring to his status as the father of the gods). But the original name survives in jovial, Jove, and most of the Romance languages’ Thursday. Most Germanic languages kept the spirit of the name. They just changed the god to Mighty Thor.
Many eastern European languages bypass the whole gods thing and just number their days. Latvian has ceturtdiena, literally quart-day (which comes after three-day). Polish, Croatian and Slovak have a variation on the word fourth—they don’t even stick day at the end, although Estonian does.
As always, Portuguese is unique for the Romance languages. Quinta-feira translates to fifth-fair, basically the fifth day after the fair, in this case meaning the day of rest, which a long time ago was the Sabbath—Saturday. Similarly, Icelandic doesn’t go by the usual thunder god-day, but fifth-day. These languages kept the tradition of numbering, with Monday as the first day of the week.
As always, there are many more languages and many more words for Thursday. This is just what I could find and understand, so imagine how much more there is out there!