The word "more rattleboned" is spelled with the IPA phonetic transcription /mɔr ˈrætlbəʊnd/. This term is characterized by the adjective "rattleboned" which means to be thin or weak. The term "more" is simply added as a comparative form. The spelling of "rattleboned" consists of the first syllable "rattle" that refers to a sound and "boned" that denotes the quality of having bones, together they create a word that refers to a thin or weak sound made by bones.
There doesn't seem to be any established etymology for the phrase "more rattleboned". Upon researching, no credible sources or dictionaries mention this specific phrase. It's possible that "more rattleboned" is an obscure or regional term that has limited usage and hasn't been extensively documented.