féth fíada(Irish: féth fíada, féth fiada, feth fiadha, fé fíada, faeth fiadha), in Irish Mythology is a magic mist or veil which the Tuatha Dé Danann uses to enshroud themselves, rendering their presence invisible to human eyesight. féth denotes this mist in particular, and fíada originally meant "knower", then came to mean "lord, master, possessor".
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 which Sidhe (fairy mound) they should dwell in, raising the feth fiada to conceal themselves from mortal men.
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]", but an ensuing passage soon after offers a rational explanation, that "..it was as a sea-expedition the Tuatha De Danann came to Ireland, and burnt their ships. It was owing to the fog of smoke that rose from them as they were burning that others have said that they came in a fog of smoke".
The miraculous powers of the feth Fiada have come to be ascribed to Christian saints. An allusion to this is found in a certain hymn whose composition was attributed to St. Patrick. The hymn is accompanied by a prose explanation of how it came to be created. 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. But then Patrick chanted this hymn, which caused the king's pursuers to mistake Patrick for deer and fawns. The hymn was given the title Fáeth Fiada, said to mean "Deer's Cry", though the phrase manifestly derives from the magic mist féth fíada。
The magic mist is also called by another name meaning Druidical Mist (Old Irish: ceo druidechta; Modern Irish: ceo draoidheachte [cʲoː drɯɪʲaxtʲə] (?)) and an example of its usage can be found in the Ulster Cycle tale Fled Bricrinn ("The Feast of Bricriu")。
See also 
- "1 féth: A magic mist, veil, which renders those under it invisible (Cf. the Germ. Tarn- kappe) the secret of which was possessed by the Tuatha D.D.: " (eDIL)
- "fíada.. orig. a part. pres. = `Knower' .. A lord, master, possessor: .. (eDIL) "
- Mackillop 1998,p.217. Lists various alternate spellings of féth fiada.
- Dobbs 1929, Altrom Tighe Da Medar, "in Feth Fiadha", p.192; tr. p.193 (also Feth Fiar, Fed Fiar)
- Mackillop 1998
- Macalister ed. tr. ¶321,322,327
- Mackillop 1998"The power was thought to have passed to Christian saints."
- faíd "cry, outcry" + gen. of 2 fíad "Wild animals, game, esp. deer"eDIL
- Stokes & Strachan 1901, vol.2, p.xl (commentary) "VII. Patrick's Hymn... The title fáeth fiada, is a misspelling of fóid (Cymr. gwaedd) fiada, and this is still further corrupted in the feth fia of the Bok of Ballymote, 345b 26, where wizards are said to make feth fia ('magical invisibility'), p.354- (prose and hymn, text and translation)
- eDIL: "1 féth:.. The name fáeth fiada (Hy vii pref → Thes. ii 354.10 ; fáed f.¤, Trip. 48.7 ) given to the hymn composed by St. Patrick .. is prob. the same expression".
- Mackillop 1998
- Henderson 1899, FB §39 (p.48)
- Mackillop, James (1998), Dictionary of Celtic Mytholgy, Oxford: Oxford University Press, ISBN 0-19-280120-1
- Dobbs, Margaret E. (1929), "Altrom Tighi da Meadar (The Fosterage of the House of Two Goblets)" (snippet), Zeitschrift für Celtische Philologie 18: 187–230 (ed. & tr.) (CLC, English)
- Stokes, Whitley; Strachan, John (1901), "Patrick's Hymn" (google), Thesaurus Palaeohibernicus (Cambridge: Cambridge University Press) 2; Introduction, p.xl
- Henderson, George (1899), Fled Bricrend: the Feast of Bricriu (google), London: David Nutt