I was sending a message to my granddaughter about getting our new car today and put Dydd car newydd ! Is that correct or should it be Diwrnod?
1 Like
Dydd is ok here.
Diwrnod is used -
with numbers e.g. tri diwrnod *but see below
with general adjectives, e.g. diwrnod braf, diwrnod gwlyb
when talking about things that fill the day such as work, activities, etc. e.g. diwrnod gwaith, diwrnod gwyliau
Dydd
used with everything else:
days of the week
used with set phrases, e.g: bob dydd, drwy’r dydd, y dyddiau ’ma
*un dydd ar y tro
used for a specific day when not naming the day of the week, e.g Dydd Calan, Dydd priodas
8 Likes
Diolch 
1 Like
@siaronjames that’s the clearest explanation I’ve read anywhere! I’m going to ‘borrow’ it 
3 Likes
Am I right in remembering that diwrnod is used when you refer specifically to a 24-hour period of time? Eg in the case of a (fun!) charity 24 hour event/activity:- Yn ystod yr holl diwrnod, bydd meddyg ar gael i helpu’r nofwyr, os bydd angen.
In case they are needed at any time during the event, there will a doctor available to help the swimmers…
2 Likes
Yes, that’s right - when the context is hours of duration, diwrnod is a full 24-hours whereas dydd is just the daylight hours.
2 Likes