Early Quenya
aldamo
noun. shoulder(s), back
almo
noun. shoulder(s), back
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
The word ᴱQ. almo or aldamo “back, shoulders” appeared in the Qenya Lexicon of the 1910s under the early root ᴱ√ALA “spread”, and the longer form was an element in the name ᴱQ. Aikaldamor “Broad Back” (QL/29). This pair of words (along with deleted {alma}) reappeared in Early Qenya Word-lists of the 1920s, but there they had the gloss “shoulder” (PE16/144).
Neo-Quenya: The early root ᴱ√ALA “spread‽” was the basis for ᴱQ. alda “tree”, which in later writings was derived from ✶galadā. Thus ᴺQ. almo “shoulder” might be retained as a derivative of the later form of the root: √GAL. The sense of the later root was “grow (like plants), flourish” rather than “spread”, so this is a bit of a reach semantically, though not impossible since ✶galadā referred to broad, spreading trees as opposed to ✶ornē for tall trees (NM/349). I would use ᴺQ. almo only for “shoulder”; for “back” I recommend the neologism ᴺQ. catta.