The Old Irish: dair (Early Old Irish: daur) is related to Welsh derw(en) and to Breton derv(enn). Its Proto-Indo-European root was *dóru ("tree"), possibly a deadjectival noun of *deru-, *drew- ("hard, firm, strong, solid"). Its phonetic value is [d].

Dair forms the basis of some first names in Irish Gaelic such as Daire, Dara, Darragh and Daragh.