And the other planes, like Phyrexia (basically "land of Phyresis") seem to have etymologies for their names...
So, 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
update: personal take on a possible etymology no official etymology has been published
If your looking for etymology here goes. To really get into it you have to break the word into parts Eld( which is an old english term for senior/) and Raine (small stretch incoming which is an old english name that comes from the german name Ragin meaning council). Those eldraine meaning old council. Fits pretty well. Below is where chasing this rabbit hole took me.
This is speculation without WotC citation, but my guess would be:
First part coming from eldritch, it's own etymology described here.
Less certain about the second part (maybe it just sounded good), but in both English and French the suffix -aine means "approximately".