A word for “neck” appearing in notes written around 1967, derived from primitive aks based on the root √AKAS “neck, ridge” (PE17/92), where the ks became ch (IPA [x]). Tolkien specified that it was “referring properly only to the vertebrae (the bony part of the neck not including throat)”, so a more accurate translation might be “✱(upper) spine”. A more ordinary word for “neck” as a passage from mouth to the stomach and lungs would be lang.
Noldorin
iaeth
noun. neck
iaeth
noun. neck
sigil
noun. necklace
lhanc
noun. throat
lhanc
noun. throat
pendrad
noun. passage up or down slope, stairway
pendrath
noun. passage up or down slope, stairway
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.
Conceptual Development: There was a similar word G. gath “neck” in the Gnomish Lexicon of the 1910s from primitive ᴱ✶yatt- (GL/36), with the Gnomish sound change of initial y to g.
Neo-Sindarin: For purposes 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”].