τόμος

Greek τόμος (tómos) comes from the verb τέμνειν (témnein), meaning 'to cut.' A tomos was a piece cut off — a section, a division, a volume of a multi-part work. Aristotle's writings were divided into tomoi. The same root produced 'atom' (a-tomos, 'uncuttable'), 'anatomy' (ana-tomos, 'cutting up'), and '-ectomy' (the surgical suffix meaning 'cutting out'). The word entered Latin as tomus and Old French as tome, arriving in English by the sixteenth century.

The semantic shift is almost a reversal. In Greek, a tomos was a part of a whole — one scroll in a set, one volume of a series. In modern English, a 'tome' is the whole thing: a large, heavy, single book. The part became the whole. This happened because multi-volume works became less common as printing technology improved. A work that once required twelve scrolls could fit in one printed volume. The word that meant 'section' was reassigned to 'the entire book, especially a big one.'

The connotation shifted too. 'Tome' now implies weight — physical and intellectual. A slim novel is not a tome. A paperback thriller is not a tome. A tome is leather-bound, dense, possibly dusty, probably unfinished. The word carries an implied reader: someone ambitious, scholarly, or pretentious, depending on who is saying it. 'He was reading a massive tome' signals either respect or mockery.

The cutting metaphor connects tome to surgery and physics. A tomography scan (CT, PET) creates images by cutting through the body in slices — tomos. An atom is what you get when you cannot cut anymore. A tome is what you cut from a library. The Greek knife is everywhere in English, and most speakers have no idea it is cutting.