Where does “Kathina” come from?

Kathina (English) comes from Pali kaṭhina, from Sanskrit कठिन, from Sanskrit कठ् — to live in distress.

Ancestry of “Kathina”, step by step

Step	Language	Word	Meaning
1	Pali	kaṭhina	embroidery hoop
2	Sanskrit	कठिन	difficult; stiff, hard, firm; harsh, cruel,...
3	Sanskrit	कठ्	to live in distress

Kathina — Etymology, Origin & Word History | Etymology Explorer