Where does “มุม” come from?

มุม (Thai) comes from Khmer មុម, from Proto-Mon-Khmer mum — corner; angle.

มุม (Thai): corner; angle

Definitions

Step	Language	Word	Meaning
1	Khmer	មុម	corner; angle
2	Proto-Mon-Khmer	mum	corner; angle

มุม — Etymology, Origin & Word History | Etymology Explorer