A word appearing as ᴱN. amoth “shoulder” in Early Noldorin Word-lists of 1920s derived from ᴱ✶a-mbod-t’ (PE13/137, 159) and related to ᴱN. bost “back” (PE13/139). In these documents amoth was an element in the name ᴱN. Egallmoth “He of the Wide Shoulders” with an initial element of ᴱN. egall “very broad” (PE13/142, PE13/159).
In the Gnomish Lexicon of the 1910s, the name G. Egalmoth was glossed “Broad-back” and it contained G. alm “back, shoulders” from primitive ᴱ✶alđam- (GL/19), while in Gnomish Lexicon slips modifying this document, the word for “a shoulder” was G. {awlan >>} alan derived from ᴱ✶aldǝmā (PE13/109). These 1910s words were probably based on the early root ᴱ√ALA “spread”, from which ᴱQ. almo or aldamo “back, shoulders” was derived (QL/29).
In Tolkien’s later writings, S. Egalmoth was given an entirely new etymology as “Pointed Helm-crest” (WJ/318).
Neo-Sindarin: Despite the change in the meaning of Egalmoth, I think ᴺS. amoth “shoulder” can be retained for purposes of Neo-Sindarin, reconceived as a derivative of √AM “up” (< ✱ammots-) and perhaps originally an augmentative using the suffix -oth = “✱most up (part of the torso)”.
A verb in the Gnomish Lexicon of the 1910s appearing as G. amra- “go up and down; live in the mountains; roam, wander”, probably a verb form of G. am “up(wards)” (GL/19). A similar verb appeared in the Early Noldorin Dictionary of the 1920s as ᴱN. amró that Tolkien described as an “old irregular verb”, of which the modern form was ᴱN. rhosta- or amrosta- (PE13/159). These 1920s verbs appeared under the entry for ᴱN. amrost “rising” functioning as the infinitive form of these verbs, so these 1920s verbs probably meant “✱to rise”. See the entry for N. eria- for later verbs meaning “rise”.