Type Word Usage Old Irish Meaning & History Old Irish word meaning "peace" or "fairy mound, tumulus", both from a root meaning "to sit" [1] . Related ItemsFamily Tree ·Details Other Languages & Culturessedom (Old Celtic) hedd (Old Welsh) Given Name DescendantsSíomha (Irish) Sítheach (Medieval Irish) Síthmaith (Old Irish) Surname DescendantsMac Síthigh, McSheehy, Sheehy (Irish) Same Spellingsid Sources & ReferencesShow Inline Numbers Hide Inline Numbers Matasović, Ranko. Etymological Dictionary of Proto-Celtic. Brill, 2009, page 326. Share on Facebook Share on Twitter Entry updated May 26, 2026