Where does “ثنين” come from?

ثنين (Malay) comes from Arabic الاِثْنَيْن, from Arabic اِثْنَان — two.

Ancestry of “ثنين”, step by step

Step	Language	Word	Meaning
1	Arabic	الاِثْنَيْن	—
2	Arabic	اِثْنَان	two

ثنين — Etymology, Origin & Word History | Etymology Explorer