Welsh Expression.
Nadolig comes from old latin which means birthday.
since the welsh for birthday is Penblwydd, this use of 'birthday' is a specific birthday, the birthday of Christ. It casually means
Christmas, but of course the word
Christmas doesn'
t literally mean birthday at all.
Llawen means joyful or merry, so Nadolig Llawen is literally merry birthday, and casually means merry xmas.