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!