From Wiktionary, the free dictionary
From English mun, dialect from of English man.
mỳn m (uncountable)
- (slang) man, mun, mate, dude (term of address, usually to a male)
- Synonyms: achan, mêt, was
Beth sy’n bod arnot ti, mỳn?!- What’s wrong with you, mun?!
