Originally, this term was used for the Elves who never saw the light of the Two Trees of Valinor (S/51, WJ/361). Later, the meaning of this term was modified to exclude the Sindar, and so became more or less equivalent to Avari (WJ/373, SI/Moriquendi). It is a compound of morë (mori-) “darkness” and the plural of Quendë “Elf”.
Conceptual Development: One of the earliest name for the Dark Elves may have been ᴱQ. Hisildi “Twilight People” (LT1/232). The term ᴹQ. Moriqendi first appeared in Silmarillion drafts from the 1930s (LR/197). It also appeared in The Etymologies, with the same derivation as given above (Ety/MOR). In this earlier period, Tolkien also used the terms ᴹQ. Moreldar and ᴹQ. Morimor for “Dark-elves” (LR/197, 405; Ety/MOR).
A singular form, Moriq(u)en, appeared in linguistic notes from the 1930s and 1940s (PE19/59; PE21/69), as an illustration of the loss of short final vowels in trisyllabic or longer words. A longer singular form Moriquende, reformed from the independent word Quendë, also appeared (PE19/59).
Elves of the Dark