What's the etymology of the name Eldraine?
I think the name comes from two words, Old and Land.

Eld is part of the word "elder". Other answers think that it relates to "Eldritch" but "Eldritch" also just means old. 

Raine is like in "Ukraine" which literately translates to Borderland
From Wiktionary


  1651 Ukrain, 1671 Ukraine, 1688 Ucrania, Ukrania, 1762 Ocraine.
  Adaptation of Polish Ukraina, Russian Украи́на (Ukraína), or Ukrainian
  Украї́на (Ukrajína), from the specific use, originally meaning
  “borderland”


Now clearly Wizards took liberty with this. I am not sure the R in the world was taken correctly, but in our minds "-ania" is a place, and many fantasy writers use this. 

So the game Land of Old fits perfectly for a place full of Arthurian knights and fairy tales