A thought occurred to me recently. That in itself could have been construed as unusual, but read on; it gets stranger: I suddenly realised that the word “week” yn Gymraeg is actually two words cunningly fused together: “wyth and nos”. Except that this literally translates as “eight nights.” Since this strange synaptic cataclysm occurred I have been wrestling with the notion that a week could have eight nights in it: and I have to say that I have concluded that it can’t. You might get away with it if it was an isolated week - perhaps a bwtcamp for instance - where the ever increasing mounds of empty Reverend James bottles and the raucous and incessant singing of Elvis in Welsh might give the illusion that there was actually an additional nos, borrowed from the week before, but, if you have a run of several weeks together: they can’t all have an extra one unless Cymru is in a different orbit to the rest of the world, perhaps spending longer on the dark side of the moon, which might explain why it rains so much. Perhaps we should be on Greenwich Amser Cymru. Or was it that God needed an extra night’s rest after all the mountain and sheep making involved?
I wonder therefore why it isn’t “saithnos”? I will gladly hand over at this point to the SSIW horological boffins.
Nic
I seem to remember a Beatles song had 8 days a week in it. Perhaps they were Welsh Scousers?
There are two things at play here.
- In ancient Celtic culture, the day began at sundown.
- It took Europe a while to figure out the concept of zero, so they started counting with one marking the beginning rather than zero.
So if you take these into account the span of one week will have 8 nights in it.
Mae hynny yn diddorol iawn Craig ond; if the day begins at sundown on the first day, it should also end at sundown on the seventh day, so it would still be saith nos. Otherwise, you are always borrowing a nos from another week and you eventually run out of noses; I mean nosen. Efallai, in those days, they simply weren’t keeping count and, perhaps that’s why they didn’t defeat Edward the 1st. Perhaps they agreed to fight him in three weeks and found they were three nights too late. By then, he had already built Castell Rhuddlan and it was all over bar the gweiddi. Well it’s only a theory, but a pretty shrewd one I would vouch.
Nic
Don’t think of it as a duration of an entire night. Think of it as end points. The week starts at night and ends at night. So yeah, the end point of one week is the end start of the next so it is effectively counted twice in that respect if you try and add them together.
If you know music, the same concept is applied in terms of an octave. A-G is seven notes but the whole octave is A-A, 8 notes. But two octaves is 15 notes. So, they found ways around it.
I’m glad you mentioned this Nic because I thought I was hearing things when Aran told me that a week was literally 8 nos…but as with everything Aran, he said it so calmly and reassuringly…(don’t worry about it)…that I actually thought the rest of the world must be wrong somehow for believing it to be 7!
And a “fortnight” in Welsh is “pythefnos”, which if you sort of screw your eyes up and look sideways can just about be recognised as “pymtheg nos”… 
At least Welsh puts a number on it; English ‘week’ is derived from a word meaning just a ‘sequence, turn’ 
Wiki pedia says that the ancient Romans traditionally used the eight-day nundinal cycle (based on Etruscan use), could it be derived from that one? That explanation would make sense to me.
I wake early Monday morning, with a four year old’s foot in my mouth. It’s dark outside. The week has begun already, and the day will dawn later.
I get to the end of Monday. I’m longing for my bed. Night falls, and some time later the children go to sleep. It’s night again, thank heavens, for the second time this week…
And the rest of it follows on from there… 
Does this explain why calan is the first day of the month but nos galan is New Year’s Eve?
I think Nos Galan maps to New Years Eve pretty well. i.e. It’s the night before New Years Day (Dydd Calan).
Although technically our ‘day’ starts at night as well (Midnight), we think of the day as beginning in the morning.
Thanks to wyth nos I keep thinking that ‘wyth’ is seven!
If you think of a day as a “fence panel”, then for seven fence panels you need eight fence posts…
That’s a good analogy, Neville, and it gives us some insight into how they viewed day and night i.e not as equal divisions of 12 hours, but the night being a gap that had to be endured between the more important days. Perhaps if Celts had been on an 18-30 holiday to the Canary Islands, they may have felt the reverse to be true and we would have the word, ‘wythdiwrnod’ instead!