A noun in The Etymologies of the 1930s glossed “cave”, apparently a combination of N. gath “cavern” and ᴹ√ROT “tunnel” (Ety/GAT(H)). Its initial element also appeared in the name N. Doriath “Land of the Cave”, but in later writings S. Doriath was redefined as “Land of the Fence” with final element S. iath “fence” (WJ/370), so N. gathrod “cave” was probably abandoned.
Noldorin
tunn
noun. hill, mound
tunn
noun. hill, mound
tund
noun. hill, mound
groth
noun. cave, tunnel
roth
noun. cave, tunnel, cave, tunnel, [G.] grot
gathrod
noun. cave
amon
noun. hill, steep-sided mount
amon
noun. hill
borth
?. [unglossed]
clei
?. [unglossed]
coen
?. [unglossed]
dath
noun. hole, pit, steep fall, abyss
diragas
?. [unglossed]
fela
noun. cave
fela
noun. cave
gas
noun. hole, gap
gathrod
noun. cave
mauth
?. [unglossed]
menwed
?. [unglossed]
mindon
noun. isolated hill, especially a hill with a watch tower
mindon
noun. tower
nith
?. [unglossed]
nithrad
?. [unglossed]
níth
?. [unglossed]
porennin
?. [unglossed]
rhond
noun. cave roof
rhond
noun. vaulted or arched roof, as seen from below (and usually not visible from outside), or a (large) hall of chamber so roofed
rhonn
noun. cave roof
rhonn
noun. vaulted or arched roof, as seen from below (and usually not visible from outside), or a (large) hall of chamber so roofed
rond
noun. cave
telwen
?. [unglossed]
ters
noun. (fine pierced) hole
tess
noun. (fine pierced) hole
torech
noun. hole, excavation, lair
N. tunn “hill, mound” appeared in The Etymologies of the 1930s as a derivative of the root ᴹ√TUN (Ety/TUN). Tolkien’s continued use of Q. Túna for the name of a hill in Valinor implies the ongoing validity of its root, so perhaps this word remained valid as well.
Conceptual Development: The word ᴱN. tûn “mound, bare hill” appeared in Early Noldorin Word-lists of the 1920s (PE13/154). G. tûn also appeared in the Gnomish Lexicon of the 1910s, but there it was unglossed and had no obvious cognates, so it is not clear what Tolkien intended it to mean (GL/72).
Neo-Sindarin: In keeping with the rule whereby nd was retained “at the end of fully accented monosyllables” (LotR/1115), I’d represent this form as ᴺS. tund in Neo-Sindarin.