Just stumbled onto this book, which is going right to the top of my wishlist:
The Ring of Words : Tolkien and the Oxford English Dictionary
From Amazon's book description:
"Tolkien's first job, on returning home from World War I, was as an assistant on the staff of the OED. He later said that he had 'learned more in those two years than in any other equal part of his life.' The Ring of Words reveals how his professional work on the Oxford English Dictionary influenced Tolkien's creative use of language in his fictional world.
"Here three senior editors of the OED offer an intriguing exploration of Tolkien's career as a lexicographer and illuminate his creativity as a word user and word creator. The centerpiece of the book is a wonderful collection of 'word studies' which will delight the heart of Ring fans and word lovers everywhere."
Contents (from the page at Oxford U. Press):
1 Tolkien as Lexicographer
2 Tolkien as Wordwright
3 Word Studies
Epilogue: Tolkien's influence on the English Language