Where does “Kế Sách” come from?

Kế Sách (Vietnamese) comes from Khmer ខ្សាច់, from Proto-Austroasiatic *skaːcʔ.

Ancestry of “Kế Sách”, step by step

Step	Language	Word	Meaning
1	Khmer	ខ្សាច់	sand
2	Proto-Austroasiatic	*skaːcʔ	—

Kế Sách — Etymology, Origin & Word History | Etymology Explorer