Mid 19th century; earliest use found in The Zoologist: a miscellany of natural history. From scientific Latin aedeagus from ancient Greek αἰδοῖα genitals, plural of αἰδοῖον, use as noun of neuter of αἰδοῖος having a claim to regard, reverence, or compassion + ἀγός leader from ἄγειν to lead.