tywydd - weather
You could use tywyll (dark), though. Nos is a feminine noun, so causes soft mutation of following adjectives:
- Nos dywyll dawel
Yes, assuming to mean "Tywyll" (dark) as opposed to "Tywydd" (weather). Also note that it would need to be "dywyll" since "Nos" is a feminine noun. I'll check if we have it in the system now and if we don't I'll add it. Edit: this is a zombie sentence and cannot be edited.