Dell

Originally any deep hole or pit, the current meaning of a small lush valley is related to “dale”.

  • 06.004 and there were dells below the level of the path overhung with bushes
  • 06.004 in one of these dells under the bushes people were talking.
  • 06.006 as he crawled into the bushes at the edge of the dell.
  • 13.064 and before long came to a deep dell

“dell, n.1.” OED Online. Oxford University Press, June 2015. Web. 27 July 2015.

Deep-set

Two common words comprise this uncommon hyphenated one, which is attested in OED.  The examples there include one word, one hyphenated word, and one compound word.

  • 01.002 deep-set round windows looking over his garden,

“deep-set, adj.” OED Online. Oxford University Press, June 2017. Web. 7 September 2017.

Deep-elves

“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.