One of the Towers of the Teeth along with its companion Narchost (LotR/900), translated “Fang Fort” in Tolkien’s “Unfinished Index” of The Lord of the Rings (RC/601). This name is a combination of carch “fang” and ost “fort(ress)” (SA/carak).
Conceptual Development: When it was first named specifically in Lord of the Rings drafts from the 1940s, this fort was already called N. Carchost (SD/23), though the earlier names N. Gorgos “Dire-castle” (TI/344) and N. Kirith Naglath “Cleft of the Teeth” (WR/137) may have been precursors to this name.
carch (“tooth, fang”) + ost (“fortress, stronghold”)