Etymology of 'nameday'

[MistakeNot]

So then, why would it be called nameday in Eorzea to this day, if it functions the same as a birthday? It seems like we're missing something that caused the term nameday to be used rather than birthday at one point if this is the case. How did the word come to be used, and how did its meaning change to what it is today?

There is nothing to indicate that nameday and birthday mean the same thing, is there?
Nameday seems to reference the day a person got their name, which may or may not be the same day they were born.