Old English -ælfen (n.) "an elf or fairy" (see elf). Not a pure adjective in Middle English (see elvish was used), but used in phrases such as elven land (c.1300). Apparently revived as an adjective by Tolkien.
Examples from the Web for elven
Thus the forest of Paimpont extended over more than twenty parishes; some say it even crossed the river, and went as far as Elven.Breton Legends|Anonymous
We rode through the forest together to one of the most magnificent monuments in Brittany, the Castle of Elven.
But this affair at the Castle of Elven is something I had not reckoned on.
Your Sylvia is not my Sylvia; the world is wide and Elven is not unknown.The King in Yellow|Robert W. Chambers