Early iterations of the Elvish languages had a number of different words for “chest” and “breast”. The Gnomish Lexicon of the 1910s had G. am² “breast, front (chest)” (GL/19), a word that reappeared in Gnomish Lexicon Slips modifying that document along with a longer variant amoth, but with only a single gloss “breast” (PE13/109). The lexicon (but not the slips) had a longer word G. {ambos >>} ammos “byrne, hauberk, cuirass”, an element in the word G. ammogrint or crinthammos “red-breast = robin” (GL/19, 27). Early Noldorin Word-lists of the 1920s had ᴱN. amb, am “breast” along with longer amuith “breast”, as well as ᴱN. am(b)os “breastplate”, but all these forms were rejected.

Neo-Sindarin: For purposes of Neo-Sindarin, I would retain ᴺS. ammos but with the sense “breast, chest” rather than “breastplate”, to serve as the cognate of ᴺQ. ambos (ambor-) “chest”; the Sindarin variant must have been derived from a primitive form with a double-s: amboss-. It might be an ancient combination of √AM “up” and ᴹ√OS “around”, perhaps with the original sense “upper enclosure (of the body)”.