"Sunday night"

Translation: nos Sul

[JettyJ]

Why not Nos dydd Sul?

[Anneke69]

Both are possible I think. Nos Sul is abbreviated.

[SirFurboy]

No, "dydd" is day (think "daytime"). "Nos" is night. Nos dydd Sul would be "Sunday day night". English merges "day" with the name of the day and makes them inseparable, so "Sunday night" is ok, but if you think about it, it is weird! Welsh doesn't do it that way. There are phrases that just use "Sul" on its own, but when referring to Sunday you must say "Sun(day) Day" or "Sun(day) Night".