Often, words that were <v> in Latin, which made their way into the Celtic languages, became <gw> in the Brythonic languages (Welsh, Breton and Cornish.) Other examples are vinum becoming gwin (wine) and viridis becoming gwyrdd (green). I had a hard time remembering Gwener - but then remembered this trait and saw the link to Venerdì, Vendredi, Viernes. Thought I'd share in case this is helpful to someone else too :D.
To those whom this tip helped, dim problem :)
Doshia2: V was pronounced W in classical times, but <> denotes orthography, not phonology, which is // or . Thus, <Cymru> /ˈkəm.ri/ or <vīnum> /ˈwiː.num/.
Can you give me some examples of what you mean?
dydd Gwener = "the day of Friday" i.e. "Friday daytime"
nos Wener = "the night of Friday" i.e. "Friday night"
bore (dydd) Gwener = "the morning (of the day) of Friday" i.e. "Friday morning"
prynhawn (dydd) Gwener = "the afternoon (of the day) of Friday" i.e. "Friday afternoon"
Stuff like that?
Yes, why are both bore Gwener and bore dydd Gwener correct? And (more importantly) when do I use which?
They're both correct because they both make literal sense:
bore dydd Gwener = "the morning of the day of Friday"
bore Gwener = "the morning of Friday"
i.e. both are valid translations of "Friday morning"
You can use both equally. They're both very common.