Later at university, Tolkien encountered some works in Old English that he hadn’t heard of previously.
Among these was the Crist of Cynewulf, a group of Anglo-Saxon religious poems. Two lines from it struck him forceibly:
Eala Earendel engla beorhtast
ofer middangeard monnum sended.
“Hail Earendel, brightst of angels/above the middle-earth sent unto men”
-Humphrey Carpenter, J.R.R. Tolkien: A Biography, p.72
Whoa, wait a minute. There we have “Middle Earth”, the name of his entire world and history, and Earendel, one of the chief Valar in his mythology. They were not always made from whole cloth but lifted from other sources.
In fact, this is one reason why Tolkien’s fantasy works and that of so many sci-fi authors do not. Their mythology is too new. It’s not connected enough to man’s (the reader’s) own history. Except that it IS, though in all the wrong ways. Ways the author’s are unaware of, especially in regards to language and the names of their characters.
Later, Tolkien was reading The House of the Wolfings by William Morris, which is written in Welsh.
Written partly in prose and partly in verse, it centres on House or famly-tribe that dwells by a great river in a clearing of the forest named Mirkwood, a name take from ancient Germaic geography and legend.
There’s another one. Mirkwood lies in the east of course. Just like in Germany. Just like it does in Middle Earth.
A hundred times over when you see a word or especially a name in Tolkien’s writing, it was very carefully chosen, following Owen Barfield’s principals I think, to evoke other qualities from the deep past of etymology, even if you aren’t fully aware of it consciencely.