Formal:
* Modryb Fawr (literally "Big/Great Aunt") - This is the most common and formal way to say "Great Aunt" in Welsh.
Informal:
* Hen Modryb (literally "Old Aunt") - This is a more informal way to refer to a Great Aunt, particularly if you are close to her.
* Modryb-Fawr - This is a less common but still acceptable way to say "Great Aunt" in Welsh. It combines the "Modryb" (Aunt) with the "Fawr" (Great).
Other options:
* You can also use the person's name directly, followed by "Modryb Fawr" or "Hen Modryb". For example, "Gwenllian, Modryb Fawr" or "Eira, Hen Modryb".
The best way to say "Great Aunt" in Welsh will depend on the specific context and your relationship with the person you are referring to.