The Etymology of Defunct
Defunct entered English in the late 16th century, taken almost unchanged from Latin defunctus. The Latin verb defungi means to discharge or complete one’s duties — built from de- (completely, off) and fungi (to perform, perform a duty). The past participle defunctus thus literally meant having performed, having discharged, and by extension having completed life itself — a euphemism for deceased that carries a quiet dignity, suggesting that death is the completion of one’s appointed role rather than a mere ending. English took both senses: defunct can describe a person (now archaic — the defunct lord), but more commonly today describes institutions, companies, treaties, machines, or laws that have ceased to function — a defunct railway, a defunct dictionary, a defunct theory. The Latin verb fungi has done remarkable work in English: it gives us function (the performing of a role), perfunctory (done only for form’s sake), and fungible (interchangeable in performing a role, as in fungible commodities). The kingdom of fungi is unrelated — that is from a different Latin word for mushroom.