Étaín or Édaín (Modern Irish spelling: Éadaoin) is a figure of Irish mythology, best known as the heroine of (The Wooing Of Étaín), one of the oldest and richest stories of the Mythological Cycle. She also figures in the Middle Irish Togail Bruidne Dá Derga (The Destruction of Da Derga's Hostel). T. F. O'Rahilly identified her as a sun goddess.
The name Étaín (Old Irish pronunciation: [eːdainʲ]) is alternately spelt as Edain, Aideen, Etaoin, Éadaoin, Aedín, or Adaon. It is derived from a diminutive form of Old Irish ét, "passion, jealousy". She is sometimes known by the epithet Echraide, ("horse rider"), suggesting links with horse deities and figures such as the Welsh Rhiannon and the Gaulish Epona. In Tochmarc Étaíne Midir names her Bé Find (Fair Woman). However, the poem embedded in the text, "A Bé Find in ragha lium" may be an older, unrelated composition that was appended to the story later.
In , Étaín is the daughter of Ailill, king of the Ulaid. A slightly different genealogy is told in Togail Bruidne Dá Derga (The Destruction of Da Derga's Hostel). Here she is the daughter of Étar, and marries the High King Eochaid Feidlech. They have a daughter, called Étaín Óg (Étaín the Younger), who marries Cormac, king of Ulster. She bears him a daughter, Mess Buachalla, but no sons. Cormac abandons Mess Buachalla, but she is found and brought up by a herdsman. When she grows up she marries the High King Eterscél and becomes the mother of Conaire Mor. In genealogical tracts she is said to have been the wife of the Ulster prince Cormac Cond Longas.