The cave-palace of Thingol in Doriath, translated “Thousand Caves” (S/56). It is a combination of meneg “thousand” and groth “cave” (SA/groth, WJ/415).
Conceptual Development: The name Ilk. Menegroth appeared in Silmarillion drafts from the 1930s (LR/114, LR/220), and was designated as Doriathrin [Ilkorin] in The Etymologies, where it had essentially the same derivation as given above (Ety/ROD). In one late note the name was given as Menegrond, which might be a “pure Sindarin” form of this name as suggested by Carl Hostetter (NM/365).
meneg (#probably “thousand”) + groth (“large underground dwelling”)