One of the Towers of the Teeth along with its companion Carchost (LotR/900), translated “Bitter-biting Fort” in Tolkien’s “Unfinished Index” of The Lord of the Rings (RC/601). This name is a combination of narch “fang” and ost “fort(ress)”.
Conceptual Development: When it was first named specifically in Lord of the Rings drafts from the 1940s, this fort was already called N. Narchost (SD/23). The earlier name N. Nargos may have been a precursor to this name (TI/344), although that name referred to a fort near Cirith Ungol rather than the Gates of Mordor.
A word appearing as an element in the name Narchost, which was glossed “Bitter-biting Fort” in Tolkien’s “Unfinished Index” of The Lord of the Rings (RC/601).
Possible Etymology: This word resembles the derivatives of the root ᴹ√NARAK from The Etymologies (Ety/NÁRAK), and probably has a similar derivation. It might be a cognate of the Quenya adjective [ᴹQ.] naraka “harsh, rending, violent (of sounds)”. Alternately, it resembles ᴱQ. narka in the Qenya Lexicon from the 1910s, whose root ᴱ√ŊARA also has the derivative ᴱQ. narte “bitter”. It could be a later restoration of those ideas.
Conceptual Development: The name N. Narch appears in Lord of the Rings drafts as the original name of the valley of Udûn in Mordor (SD/34), but it isn’t clear whether Tolkien intended this name to be related to Narchost.