The word has clear Finnic cognates, especially Estonian hiis ‘(sacred) grove / sacred place’, and related forms (e.g., Estonian hiid ‘giant’). It also has several Finnish and Finnic derivatives (notably hitto, hiitto, and others), reflecting later semantic developments and taboo-avoidance strategies typical of “power words.” The Finnic term has been borrowed into North Sámi (e.g., hiiˈdâ ‘devil’), indicating later contact and spread of the demonized sense. A prominent hypothesis links Finnic hiisi to a Scandinavian/Germanic word-family meaning something like a lair / resting place / hide, with a plausible semantic bridge via “place of lying/resting,” “grave/burial place,” “cult place.”