The Ring of Words: Tolkien and the Oxford English Dictionary by Peter Gilliver, Jeremy Marshall, and Edmund Weiner, discusses Tolkien's involvement with the O.E.D. as a recently de-mobbed vet and goes on to examine the particular "word-hoard" created by this titan of Fantasy literature. The book is a welcome resource for anyone who takes seriously Tolkien's assertion that the Lord of the Rings was primarily linguistic in inspiration. Tolkien created the world of his stories to support his invented languages. In writing those stories in English, then, Tolkien also worked to create a "poetic diction" that would impart the necessary "flavor" and shades of meaning to support the invented languages. The Ring of Words is a short, concise look at this central aspect of Tolkien's creative process and a consideration of its unintended effect on the English language.
If you have read The Lord of the Rings, then this work stands on its own, but it also makes a nice companion piece with Tom Shippey's Road to Middle Earth. Though I have issues with her synthesis, The Ring of Words may also pair well with Verlyn Flieger's Splintered Light: Logos and Language in Tolkien's World.