Type Word Usage Old Irish Meaning & History Old Irish prefix meaning "good" [1] . Related ItemsFamily Tree ·Details Other Languages & Culturesdagos (Old Celtic) da (Old Welsh) Given Name DescendantDagda (Irish Mythology) Same Spellingdag 1 Sources & ReferencesShow Inline Numbers Hide Inline Numbers Matasović, Ranko. Etymological Dictionary of Proto-Celtic. Brill, 2009, page 86. Share on Facebook Share on Twitter Entry added May 26, 2026