Where does “คู่สมรส” come from?

คู่สมรส (Thai) comes from Thai คู่, from Proto-Tai ɡuːᴮ — pair.

คู่สมรส (Thai): spouse

Definitions

Step	Language	Word	Meaning
1	Thai	คู่	pair; even number; couple; partner
2	Proto-Tai	ɡuːᴮ	pair

คู่สมรส — Etymology, Origin & Word History | Etymology Explorer