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c.1600, from Latin septicus "of or pertaining to putrefaction," from Greek septikos "characterized by putrefaction," from sepein "make rotten or putrid, cause to rot" (see sepsis). Septic tank is attested from 1902.
septic sep·tic (sěp'tĭk)
Of, relating to, having the nature of, or affected by sepsis.
Causing or producing sepsis; putrefactive.
A severe infection caused by pathogenic organisms, especially bacteria, in the blood or tissues. If untreated, a localized infection, as in the respiratory or urinary tracts, can lead to infection in the bloodstream and widespread inflammation, characterized initially by fever, chills, and other symptoms and later by septic shock.