• 10.003 to the mountain-shadowed plains beyond,

This concept does not have an entry in OED, whether hyphenated or not.

Mountains have roots, but there is only one instance of “mountain-roots”.

• 12.021 he shook the mountain-roots.

Here are other forms of this concept:

• 05.012 down at the very roots of the mountain.
• 12.012 right at the Mountain’s root.
• 12.096 beneath the roots of the Mountain,

The Roots of the Mountains: Wherein is Told Somewhat of the Lives of the Med of Burgdale, their Friends, Their Neighbors, Their Foemen, and Their Fellows-in-Arms, by William Morris, is the earliest that I know where to look for this idea.  Famous Tolkien scholar Douglas A. Anderson reported that “Lewis writes that Tolkien ‘grew up on William Morris and George MacDonald.'”  I am about to send a note to that eminent gentleman to ascertain his source.  Update just two hours later – Dr. Anderson has kindly replied that “the quote comes from a CS Lewis letter to Arthur Greeves, dated 4 February 1933. It’s in They Stand Together (p. 449), and also (I suppose) the Collected Letters of CSL.”  I will endeavor to put my hands on one book or the other forthwith.

Meanwhile, “mountain-root” by any spelling is not found in OED, so we will give it the JRRT tag.  And by “we”, I mean “the dogs and I”.

Anderson, Douglas A. Personal correspondence. September 19, 2017. email.

Anderson, Douglas A. “Week 3 Friday Lecture.” Roots of the Mountain.  Course for Signum University, lecture delivered September 12, 2014. Web.

• 04.024 since his horse was not suitable for the mountain-paths.

Although “mountain path” has a sub-entry under “mountain” in OED, both the entry and all examples have a space, not a hyphen.  I’m declaring this a JRRT original spelling.

• 12.021 out into the huge passages of the mountain-palace

A unique Tolkien-created way to put together this concept.

• 10.035 At the Mountain-king’s return!

This wonderfully nuanced word is found in OED.

 mountain king  n.

1834   F. D. Hemans Songs of Captivity iv, in National Lyrics 168   I dream of some proud bird, A bright-eyed mountain king.

1954   J. R. R. Tolkien Fellowship of Ring ii. x. 416   Like a lost child that had clambered upon the throne of mountain-kings.

2000   World & I (Electronic ed.) 1 Nov. 167   Among the Lapps, it was said that the northern lights originated in a battle between the god Thor and the mountain king.

Since there are other examples before and after, I wonder how we count this one?  I can see it both ways – and I will ask advice of you all in the blog, September 19, 2017.

UPDATE – Since the other examples do not have the hyphen, this is a JRRT original form of the word.

“mountain, n. and adj.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/122893. Accessed 19 September 2017.

• 10.008 through the mountain-gates,

Found nowhere in OED, a Tolkien original.

• 03.040 “There are moon-letters here,
• 03.041 “What are moon-letters?”
• 03.042 “Moon-letters are rune-letters,
• 11.013 and the message of the moon-letters Elrond had read.
• 11.019 about the runes or the moon-letters,

These go completely unmentioned in OED, a true JRRT original.

• 14.032 and the money-counters!’

It’s an old concept, but a new way of putting the words together, unattested in OED as a single word or compound word.

• 01.117 He turned with mock-politeness to Bilbo.

This is a new combination word, not in the OED.