The name is generally considered to be of Welsh origin (though an Old Cornish or Old Breton origin is also possible), derived from Old Welsh, Old Cornish, or Old Breton aball or avallen(n), “apple tree, fruit tree” (cf. afal in Modern Welsh, derived from Common Celtic *abalnā, literally “fruit-bearing (thing)”).[1][2][3][4][5] It is also possible that the tradition of an “apple” island among the British was related to Irish legends concerning the otherworld island home of Manannán mac Lir and Lugh, Emain Ablach (also the Old Irish poetic name for the Isle of Man),[2] where Ablach means “Having Apple Trees”[6]—derived from Old Irish aball (“apple”)—and is similar to the Middle Welsh name Afallach, which was used to replace the name Avalon in medieval Welsh translations of French and Latin Arthurian tales. All are etymologically related to the Gaulish root *aballo “fruit tree”—(as found in the place name Aballo/Aballone) and are derived from a Common Celtic *abal- “apple”, which is related at the Proto-Indo-European level to English apple, Russian яблоко (jabloko), Latvian ābele, et al.[7][8]
Source: Avalon – Wikipedia
Tim B.
“Geoffrey dealt with Avalon in more detail in the Vita Merlini, in which he describes for the first time in Arthurian legend the enchantress Morgan (Morgen) as the chief of nine sisters (Moronoe, Mazoe, Gliten, Glitonea, Gliton, Tyronoe, Thiten and Thiton)[10] who rule Avalon. Geoffrey’s description of the island indicates a sea voyage was needed to get there. His description of Avalon here, which is heavily indebted to the early medieval Spanish scholar Isidore of Seville (being mostly derived from the section on famous islands in Isidore’s famous work Etymologiae, XIV.6.8 “Fortunatae Insulae”),[11][12][13][14] “
Tim B.
https://en.wikipedia.org/wiki/%C3%8Ele_de_Sein
“Robert Graves says that the island was once home to a conclave of nine virgin priestesses believed to hold magical powers, who might be approached by those who sailed to consult them.[1]
[…] According to Breton legend, Île de Sein was once home to a group of virgin druid priestesses called the Gallizenae. They are said to have had the power to predict the future, to calm the winds, and to take the forms of different animals.[4]”