Féth fíada is a mist or veil in Irish mythology, which members of the Tuatha Dé Danann use to enshroud themselves, rendering their presence invisible to human eyesight.
[2][3] An example of usage occurs in the Altram Tige Dá Medar ("Fosterage of the House of Two Milk-Vessels"), where Manannán mac Lir makes an assignment to each member as to which Sidhe (fairy mound) they should dwell in, raising the feth fiada to conceal themselves from mortal men.
[4][5] In the Lebor Gabála Érenn, one passage declares that the Tuatha Dé Danann came "without ships or barks, in clouds of fog [over the air, by their might of druidry]",
The high king Lóegaire mac Néill, with the will to prevent the saint and his band from coming to Tara to spread the faith, sent out troops to find and intercept them.
[7] The hymn was given the title Fáeth Fiada, said to mean "Deer's Cry",[8] though the phrase manifestly derives from the magic mist féth fíada.