The exact meaning of Achilleus is unknown. Achilleus could mean “he whose people have distress” or “he who has the people distressed” (from ancient Greek “ákhos/ἄχος” = distress/sorrow/pain + “laós/λαός” = people/soldiers). Besides Achilleus could mean “thin-lipped” (from ancient Greek “a-/α-“ = negation element + “kheĩlos/χεῖλος” = lip).
