√ROT root. “cave; delve underground, dig, excavate, tunnel, [ᴹ√] bore; [ᴱ√] hollow”
The earliest iteration of this root was ᴱ√ROTO “hollow” from the Qenya Lexicon of the 1910s, with derivatives like ᴱQ. rotl “cave, hollow” and ᴱQ. rotse “pipe, tube” (QL/80). The primitive root ᴱ√roto also appeared in the contemporaneous Gnomish Lexicon with derivatives like G. rod “tube, stem” and G. †roth “cave, grot” (GL/65). The root reappeared as ᴹ√ROT “bore, tunnel” as a late addition to The Etymologies of the 1930s that Christopher Tolkien omitted from the published version of The Lost Road; it had with derivatives ᴹQ. rotto/N. (g)roth “cave, tunnel” (EtyAC/ROT), and was also an element in the name N. Nogrod (EtyAC/NAUK).
The root appeared as √ROT “cave” in notes on Words, Phrases and Passages in the Lord of the Rings from the late 1950s or early 1960s (PE17/49), as *groto “dig, excavate, tunnel” in the Quendi and Eldar essay of 1959-60 (WJ/414), as unglossed (g)roto in other notes associated with that document (VT39/9) and as rot, s-rot “delve underground, excavate, tunnel” in notes associated with The Shibboleth of Fëanor from 1968 (PM/365 note #56). Thus in later writings the root √ROT had variants √GROT and √SROT.
Neo-Eldarin: For purposes of Neo-Eldarin I would ignore the gloss “cave” which seems to be a loose translation, and stick with the meaning “excavate, tunnel, bore” for the root √ROT; I’d also retain the meaning “hollow” from the 1910s to allow salvaging similar early words from the Qenya and Gnomish Lexicon.
References ✧ PE17/49, 183; PM/352, 365; VT39/9; WJ/414-415
ᴹ√ROT root. “bore, tunnel”
References ✧ Ety/NAUK; EtyAC/ROT
ᴱ√ROTO root. “hollow”
References ✧ GL/65; LT2A/Rothwarin; QL/71, 80