Per 《
说文解字》,
甸 originally meant 'royal field' — the outer ring of the king's domain in ancient Chinese cosmography. Today the meaning survives mainly in place names:
海甸 (Haidian, Beijing's tech hub),
桦甸 (in Jilin), and crucially
缅甸 (Miǎndiàn = Myanmar/Burma) where it forms part of the country name.