Brasil (mythical island)

Brasil, also known as Hy-Brasil or several other variants, is a phantom island said to lie in the Atlantic Ocean west of Ireland. Irish myths described it as cloaked in mist except for one day every seven years, when it becomes visible but still cannot be reached.
Etymology.
The etymology of the names "Brasil" and "Hy-Brasil" is unknown, but in Irish tradition it is thought to come from the Irish "Uí Breasail" (meaning "descendants (i.e., clan) of Bresail"), one of the ancient clans of northeastern Ireland. cf. Old Irish: "Í": island; "bres": beauty, worth, great, mighty.
Despite the similarity, the name of the country Brazil, also spelled Brasil, has no connection to the mythical islands (although J. R. R. Tolkien's essay "On Fairy Stories", has likened both together.) The South American country was at first named Ilha de Vera Cruz ("Island of the True Cross") and later Terra de Santa Cruz ("Land of the Holy Cross") by the Portuguese navigators who arrived there. After some decades, it started to be called "Brazil" (Brasil, in Portuguese) due to the exploitation of native brazilwood, at that time the only export of the land. In Portuguese, brazilwood is called "pau-brasil", with the word "brasil" commonly given the etymology "red like an ember", formed from Latin "brasa" ("ember") and the suffix "-il" (from "-iculum" or "-ilium").
Appearance on maps.
Nautical charts identified an island called "Bracile" west of Ireland in the Atlantic Ocean as far back as 1325, in a portolan chart by Angelino Dulcert. Later it appeared as Insula de Brasil in the Venetian map of Andrea Bianco (1436), attached to one of the larger islands of a group of islands in the Atlantic. This was identified for a time with the modern island of Terceira in the Azores.
A Catalan chart of about 1480 labels two islands "Illa de brasil", one to the south west of Ireland (where the mythical place was supposed to be) and one south of "Illa verde" or Greenland.
On maps the island was shown as being circular, often with a central strait or river running east–west across its diameter. Despite the failure of attempts to find it, this appeared regularly on maps lying south west of Galway Bay until 1865, by which time it was called Brasil Rock.
Searches for the island.
Expeditions left Bristol in 1480 and 1481 to search for the island; and a letter written by Pedro de Ayala, shortly after the return of John Cabot (from his expedition in 1497), reports that land found by Cabot had been "discovered in the past by the men from Bristol who found Brasil".
In 1674 a Captain John Nisbet claimed to have seen the island when on a journey from France to Ireland, stating that the island was inhabited by large black rabbits and a magician who lived alone in a stone castle, yet the character and the story were a literary invention by Irish author Richard Head. Roderick O'Flaherty in "A Chorographical Description of West or H-Iar Connaught" (1684) tells us "There is now living, Morogh O'Ley (Murrough Ó Laoí), who imagines he was personally on O'Brasil for two days, and saw out of it the iles of Aran, Golamhead [by Lettermullen], Irrosbeghill, and other places of the west continent he was acquainted with."
Hy-Brasil has also been identified with Porcupine Bank, a shoal in the Atlantic Ocean about west of Ireland and discovered in 1862. As early as 1870 a paper was read to the Geological Society of Ireland suggesting this identification. The suggestion has since appeared more than once, e.g., in an 1883 edition of "Notes and Queries" and in various twentieth-century publications, one of the more recent being Graham Hancock's book "Underworld: The Mysterious Origins of Civilization".
In popular culture.
Margaret Elphinstone wrote a novel, Hy Brasil (2002), about a woman who is sent to write the first-ever travel book on Hy Brasil.
In Jack Vance's "Lyonesse Trilogy", the largest island of the Elder Isles, where the titular kingdom is located, is called "Hybras", which the prologue of the first book states to be the in-universe origin for the name of Hy-Brasil.
In the film "Erik the Viking", the characters must travel to Hy-Brasil to obtain a magical horn. Fulfillment of a curse leads to the sinking of the island.
Mary Burke's short story uses the myth as an allegory of the breach caused by the Northern Irish Troubles. Mary Burke, “Hy-Brasil” in "The Faber Best New Irish Short Stories, 2004-5" Ed. David Marcus. London: Faber & Faber, 2005, 101–05. 
In his 1867 poem "Celtic Speech," Lionel Johnson refers to it as "Holy Hy."
Hybrasil are an Irish electronica group named after the mythical island.
The island features in Geraldine McCaughrean's fantasy novel "The Stones Are Hatching".
A variation on the legend appears in the SCP Foundation article 'Peekaboo Island', in which the titular island was sealed off from the wider world by the mythical King Dyrmud at some point in the eleventh century, only re-appearing every leap year. The island is separately featured as centerpiece of a canon called "War On All Fronts," involving the invasion of the Hy-Brasil island by massive oceanic creatures.