ᴹ√(N)DUL root. “hide, conceal”
A root in The Etymologies of the 1930s given as ᴹ√DUL “hide, conceal” with a strengthened variant ᴹ√NDUL and derivatives like ᴹQ. nulla/N. doll “secret; dark, dusky, obscure” as well as N. delia- “conceal” with past participle N. dolen “hidden, secret” (Ety/DUL, NDUL). This root contributes to one of the meanings of N. Gondolin = “(Heart of) Hidden Rock” = N. gonn + dolen or N. gonn + doll + N. ind “heart” (EtyAC/GOND; Ety/DUL). Tolkien’s continued use of “Hidden Rock” as one of the translations of Gondolin in later writings indicates the ongoing validatity of the root √(N)DUL:
Or so its name [Hidden Rock] was afterwards known and interpreted; but its ancient form and meaning are in doubt. It is said that the name was given first in Quenya (for that language was spoken in Turgon’s house), and was Ondolindë, the Rock of the Music of Water, for there were fountains upon the hill. But the people (who spoke only the Sindarin tongue) altered this name to Gondolin and interpreted [it] to mean Hidden Rock: Gond dolen in their own speech (WJ/201).
References ✧ Ety/DUL, GOND, NDUL, TER
|NDUL||strengthened||✧ Ety/DUL; Ety/NDUL; Ety/TER|