The physical whole of a living thing. Also the main matter of a work, as against its head and foot.
Old English bodig (the trunk of a person or animal); unusually for so basic a word, it has no secure cognates outside English, so the trail runs no further back than this.
The whole considered as one connected mass rather than a list of its parts, whether the mass is living tissue or a document's own substance — what is lost when either kind of body is reduced to a summary, an excerpt, or a single limb standing in for it.