The historian Walter Scaife remarked in 1890 that the toponym had something of a will-o'-the-wisp character, "for on various maps it may be seen designating a great Antarctic continent, extending to the South Pole, or a small island near the Arctic Circle; or it may be as far west as the southern part of South America or as far east as the vicinity of the coast of Ireland..." The form of the name being "almost as various as the positions in which it is found..." and listing thirteen different variations thereof.

[4] It is synonymous with the Medieval Latin brasile, the term for a dye that enjoyed great popularity as a trading commodity in the twelfth century throughout Western Europe.

It has been speculated that the widespread appearance of the name served as a locational marker for sources of the dye, primarily for sailors from the Republic of Genoa where most of the maps originate.

[8] This was identified for a time with the modern island of Terceira in the Azores, where a volcanic mount at the bay of its main town, Angra do Heroismo, is still named Monte Brasil.

[11] 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.

Hy-Brasil has also been identified with Porcupine Bank, a shoal in the Atlantic Ocean about 200 kilometres (120 mi) west of Ireland[14] and discovered in 1862.