N. iaeth n. “neck” (Category: Neck)
A word for “neck” in The Etymologies of the 1930s derived from primitive ᴹ✶yakta- under the root ᴹ√YAK (Ety/KEM), where the primitive k spirantalized and vocalized to i and the resulting diphthong ai became ae, sound changes that remain plausible in Sindarin as well.
Neo-Sindarin: For purpose of Neo-Sindarin, I would use iaeth for “neck” as a joining between the head and torso, as opposed to lang as a passage from the mouth to stomach and lungs [including the “*throat”] and S. ach referring the vertebrae in the neck [“*(upper) spine”].
Reference ✧ Ety/YAK ✧ “neck”
|ᴹ✶yakta- > iaeth||[jakta] > [jaktʰa] > [jaxθa] > [jaiθa] > [jaiθ] > [jaeθ]||✧ Ety/YAK|