How did I get this question"Almost Correct"?I typed "Nos Lau" and it says that it was almost correct.
It comes from "Jove" (= Jupiter), just as French "jeudi" or Italien "giovedì" :)
Correct. Monday = Moon (e.g. dydd Llun, Lundi), Tuesday = Mars (e.g. dyed Mawrth, Marti), Wednesday = Mercury (e.g. dydd Mercher, Mecredi), Thursday = Jove (or Jupiter) (e.g. dydd Iau, Juedi), Friday = Venus (e.g. dydd Gwener, Vendredi), Saturday = Saturn (e.g. dydd Sadurwn, Samedi), Sunday = (obviously) Sun (e.g. dydd Sul, Dimanche)
If you scroll up the page a bit, you'll see that has caught many of us out at one time or another. It's actually 'Nos Iau' with a capital 'i' and not an 'L'. :-) Annoying once you spot it, or it's pointed out. :-)