A JRRT original.

• 13.036 wrought for some young elf-prince long ago.
• 16.040 You are more worthy to wear the armour of elf-princes

A JRRT original.

• 19.004 Here elf and elf-maiden

This one is a JRRT original.

• 03.033 in face as an elf-lord,
• 08.133 since he had not yet as great a treasure as other elf-lords of old.
• 17.054 and the elf-lords were at bay about their king

2016.02.04  “Elvenking” is used exclusively in Chapter 9 and onward; “Elf-king” is used only in Chapter 8.  This first reference may have been to a predecessor, the second is definitely Thranduil and “Elvenking” hereafter is exclusively Thranduil.

“Elf-king” is not attested in OED; “Elvenking” is, but in this manner, which gives all the credit to Tolkien:

2. Comb. (referring to a kind of imaginary being in the works of J. R. R. Tolkien).

a. appositive, as elven-kin.

b. attributive, as elven-king, elven-tongue; elven-wise adj.

1937   J. R. R. Tolkien Hobbit xvii. 285   But the Elvenking said: Long will I tarry.

• 08.133 for the elf-king had bargained with them to shape his raw gold
• 08.133 If the elf-king had a weakness it was for treasure,

“ˈelven, n.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/60661. Accessed 13 September 2017.

Nowhere in the OED.

• 17.005 Still the elf-host has not departed as I bade!
• 17.029 and the elf-host will go back to the Forest.
• 18.042 The elf-host was on the march;

This is found nowhere in OED.

• 09.005 and the elf-guards sang as they marched along the twisting,

Yes, this is one of the few “elf-” compounds attested in the OED.  Why?

 elf-friend  n.

1937   J. R. R. Tolkien Hobbit iii. 62   The master of the house was an elf-friend.

I’m giving him full credit for this one.

• 03.032 The master of the house was an elf-friend –
• 04.034 “Murderers and elf-friends!”
• 18.049 And I name you elf-friend
• 19.038 It is true that for ever after he remained an elf-friend,

“elf, n.1.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/60431. Accessed 13 September 2017.

A new JRRT construct.

• 17.051 and the elf-charge was halted,

A brand new JRRT construction!

• 09.051 in the elf-caves for ever.