"Bore dydd Iau"
I put "The morning of Thursday" and it was wrong. Can somebody please clarify what I did wrong?
The literal translation of 'Bore dydd Iau' is 'morning of Thursday'. This is transposed into English as 'Thursday morning'
If you wanted to add the definite article as in your suggestion then it would be Y bore dydd Iau
The dydd can be dropped when bore and prynhawn are used with the name of a day. It is always dropped when nos is used.
Welsh and English have very different structures and rules, so attempts at word-by-word translations often do not work very well.