Where does “Μέγαρα” come from?

Μέγαρα (Greek) comes from Ancient Greek Μέγαρα, from Ancient Greek μέγᾰρον.

Ancestry of “Μέγαρα”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Μέγαρα	—
2	Ancient Greek	μέγᾰρον	—

Μέγαρα — Etymology, Origin & Word History | Etymology Explorer