Achilles \ach(il)-les\ as a boy's name is pronounced a-KILL-eez. It is of Greek origin. From Achilleus. Mythology: name of the hero of the Trojan War, celebrated in Homer's "Iliad", famous for his valor and manly beauty. He was all but invulnerable, having been dipped in the River Styx by his mother, the nymph Thetis. She held him, however, by the heel, which was thus his one weak point: hence "Achilles' heel". Also a saint's name.