This hyphenated word is made from two common words.  It’s not found either hyphenated or as a compound word in the OED, so is a JRRT original for our purposes.

• 08.102 only great strands of double-thick spider-rope

“Elf” is an uncommon word.  The hyphenated combination is unattested in OED, therefore a JRRT original.  Tolkien spun out a marvelously complex tapestry of interrelations between types of Elves in his legendarium.

[08.131]  The feasting people were Wood-elves, of course.  These are not wicked folk.  If they have a fault it is distrust of strangers.  Though their magic was strong, even in those days they were wary. They differed from the High Elves of the West, and were more dangerous and less wise. For most of them (together with their scattered relations in the hills and mountains) were descended from the ancient tribes that never went to Faerie in the West. There the Light-elves and the Deep-elves and the Sea-elves went and lived for ages, and grew fairer and wiser and more learned, and invented their magic and their cunning craft in the making of beautiful xx and marvellous things, before some came back into the Wide World. In the Wide World the Wood-elves lingered in the twilight of our Sun and Moon…

• 08.131 and the Deep-elves

The Tolkien Gateway article on them may be found here.  A beautifully detailed genealogy of individuals may be found here.  Finally, a very accessible chart of the relationships between different groups of Elves may be found here.

“Dart” is an uncommon word.  Dart-throwing is unattested in OED, so JRRT original.

• 08.092 and even grown-up he had still spent a deal of his time at quoits, dart-throwing,

Two common words comprise this uncommon hyphenated one.  It’s one of my favorite colors, yet unattested in OED.

• 08.006 Worse still it brought thousands of dark-grey

Two common words comprise this uncommon hyphenated one.  It is not attested in OED, and so a JRRT original!

• 01.026 and very bright eyes under his dark-green hood.
• 02.026 and Bilbo was wearing a dark-green hood
• 02.026 and a dark-green cloak borrowed from Dwalin.

• 12.052 I am the clue-finder,

As with most names and titles in the work, there is no reference in OED, and it is now classed as JRRT original.

Constructed of one uncommon and one common word!  This one is not attested in OED as a hyphenated word at all, or even as a compound word.  JRRT gets the credit for our purposes.

• 09.004 He did not at all like the look of the cavern-mouth,