Where does “ความถ่อย” come from?

ความถ่อย (Thai) comes from Thai ความ, from Proto-Tai ɣwaːmᴬ — matter.

Ancestry of “ความถ่อย”, step by step

ความถ่อย traces back through two separate lines of ancestry.

via Thai ความ

StepLanguageWordMeaning
1Thaiความaffair; matter; content; essence; subject;...
2Proto-Taiɣwaːmᴬmatter

via Thai ถอย

StepLanguageWordMeaning
1Thaiถอยto move back, backwards, aside, or away; to cause...
2Middle Chinese退—
Every word from Proto-Tai ɣwaːmᴬ →Every word from Thai ความ →