Late 17th century. From post-classical Latin octateuchus the volume containing the first eight books of the O.T. from Byzantine Greek ὀκτάτευχος, use as noun (short for ὀκτάτευχος βίβλος) of ὀκτάτευχος containing eight books from ancient Greek ὀκτα- + τεῦχος. Compare French octateuque.