* No Direct Translation: The concept of a "fallen angel" is primarily rooted in Judeo-Christian theology. While Welsh has a rich mythology, it doesn't have a specific term for this idea.
* Descriptive Phrases: You could use descriptive phrases to convey the idea:
* Angel sydd wedi cwympo: "Angel who has fallen"
* Angel sydd wedi'i ddiswyddo: "Angel who has been dismissed"
* Angel a drodd ei gefn ar Dduw: "Angel who turned their back on God"
* Borrowing: You could use a borrowed term:
* Angel syrthiedig: This is a direct translation from English, but might not be the most common way to express it in Welsh.
It's important to remember: The specific choice of words would depend on the context and the tone you wish to convey.