Formal:
* Ffrind gorau: This is the most literal translation, meaning "best friend."
Informal:
* Ffrind agosaf: This means "closest friend," emphasizing the strong bond.
* Cymrawd: This is a more intimate term, suggesting a close confidant or soulmate.
* Ffrindiau gorau: This uses the plural form "best friends," emphasizing that you're referring to multiple people.
You could also use phrases like:
* Fy ffrind gorau: This translates to "my best friend"
* Rydym yn ffrindiau gorau: This means "we are best friends"
Ultimately, the best way to say "best friend" in Welsh depends on the context and your relationship with the person.