c. 1600, "victory involving one's own ruin," translating Greek Kadmeia nikē, from Cadmus (Greek Kadmos), legendary hero-founder of Thebes in Boeotia and bringer of the original sixteen-letter alphabet to Greece. Probably a reference to the story of Cadmus and the "Sown-Men," who fought each other till only a handful were left alive. Compare Pyrrhic (adj.1).

in ancient Greece or Rome, "herald's staff," 1590s, from Latin caduceus, alteration of Doric Greek karykeion "herald's staff," from kēryx (genitive kērykos) "a herald," probably a Pre-Greek word. Token of a peaceful embassy; originally an olive branch. Later especially the wand carried by Mercury, messenger of the gods, usually represented with two serpents twined round it and wings. Related: Caducean.

The caduceus is a symbol of peace and prosperity, and in modern times figures as a symbol of commerce, Mercury being the god of commerce. The rod represents power; the serpents represent wisdom; and the two wings, diligence and activity. [Century Dictionary]

Sometimes used mistakenly as a symbol of medicine by confusion with the Rod of Asclepius, Greek god of medicine, which also features a serpent entwined about a rod but only a single serpent.