Mid 17th century. As adjective from classical Latin octōchordos having eight strings or notes (Vitruvius) and its etymon ancient Greek ὀκτάχορδος having eight strings or notes from ὀκτα- + χορδή; compare French octacorde, octocorde. As noun from post-classical Latin octachordum, octochordum musical instrument with eight strings from Hellenistic Greek ὀκτάχορδον series of eight notes, use as noun of neuter singular of ancient Greek ὀκτάχορδος; compare French octacorde eight-stringed lyre, octocorde eight-stringed instrument, scale with eight notes.