Where does “thói quen” come from?

thói quen (Vietnamese) comes from Vietnamese thối, from Proto-Chamic *ʔadhɛ̃y, from Proto-Malayo-Polynesian daqih, from Proto-Austronesian daqiS — forehead.

thói quen (Vietnamese): habit

Definitions

habit

Ancestry of “thói quen”, step by step

thói quen traces back through two separate lines of ancestry.

via Vietnamese thối

Step	Language	Word	Meaning
1	Vietnamese	thối	rotten; fetid, putrid, stinking, foul-smelling;...
2	Proto-Chamic	*ʔadhɛ̃y	forehead
3	Proto-Malayo-Polynesian	daqih	forehead
4	Proto-Austronesian	daqiS	forehead

via Vietnamese quen

Step	Language	Word	Meaning
1	Vietnamese	quen	familiar
2	Chinese	慣	—

Every word from Proto-Austronesian daqiS →Every word from Proto-Malayo-Polynesian daqih →Every word from Proto-Chamic *ʔadhɛ̃y →