Septic

google

ref

early 17th century: via Latin from Greek sēptikos, from sēpein ‘make rotten’.

wiktionary

ref

From Ancient Greek σηπτικός(sēptikós, “characterized by putridity”), from σηπτός(sēptós), from σήπειν(sḗpein).

From Latin septem(“seven”).

Short form of Cockney rhyming slang septic tank(“Yank”).

etymonline

ref

septic (adj.)

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.