Factoid of the day

 The name Brazil could only have come to the Portuguese from the Celtic legendary name applied to the ‘islands of the blessed’, the Tír na nÓg of the land of the setting sun...

Roger Casement...put forward an argument that the origins of the name Brazil derive from the mythical Hy-Brassil...

He believed that Hy-Brassil was a name derived from the legends of the Atlantic sea-board, with Celto-Iberian origins dating from ‘Atlantis and the submerged mother-land of the early Irish, Iberians and possibly Phoenicians’...

The name Brazil as a surname is current and common to both Ireland and Portugal today

more HERE PFD
via Medievalistsnet

and more HERE:

 Brasil as shown in relation to Ireland on a map by Abraham Ortelius (1572)

 that name has been found on a contemporary Catalan (Spanish) map:

On a map from Catalonia dating back to 1480 an island can be found, named "Illa de brasil" that lies to the south west of Ireland, the supposed location of the mystical island.

or maybe not.

no, it is not named after Brazil nuts: Most Brazil nuts are not called that in Spanish or Portuguese, and anyway, most are exported from Bolivia.

But Brazil might have gotten it's name from the Brazilwood tree:  the name comes from "ember" and was originally used to describe a dye from an Asian tree.

Brazilwood was first mentioned as a dye in 1321, sourced from the East Indies and India and obtained from sappanwood trees. This red dye was in high demand throughout the Renaissance; it was traded in powder form and it was difficult to obtain.

In Medieval times, only sappanwood was available in Europe. However, in 1500 the Portuguese landed in South America and found that brazilwood trees grew in abundance along the coast. This tree was of such economic importance that the Portuguese eventually named the country after the trees found there. Brazil is the only country in the world named after a natural dye.

More HERE about the dye, the entomology of the word that was first used to describe the Asian dye,  and the Portuguese monopoly on the new source of dye that led to deforestation and it's near extinction in Brazil, along with more information about trade in those days.