Sentarse, Spanish for “to sit”, comes from the root *sed‑, meaning the same.
The surprising English cognate is… saddle. A saddle is what you do sit in, indeed!
This mapping is not obvious at first, but you can see that the s‑d root of saddle maps to the s-(n)-t of sentarse. Anglo-Saxons are shorter and to the point – as usual.
English does have another word from the same root, but it comes via the Latin and is thus more pretentious and closer to the Spanish: sedentary. A veritable SAT word!