E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The Yarrow, called by the French the herbe aux charpentiersi.e., carpenters wort, because it was supposed to heal wounds made by carpenters tools. Called Achilla from Achills, who was taught the uses and virtues of plants by Chiron the centaur. The tale is, that when the Greeks invaded Troy, Telphus, a son-in-law of King Priam, attempted to stop their landing; but Bacchus caused him to stumble over a vine, and, when he had fallen, Achills wounded him with his spear. The young Trojan was told by an oracle that Achills (meaning milfoil or yarrow) would cure the wound; but, instead of seeking the plant, he applied to the Grecian chief, and promised to conduct the host to Troy if he would cure the wound. Achills consented to do so, scraped some rust from his spear, and from the filings rose the plant milfoil, which, being applied to the wound, had the desired effect.