mid-14c., "discharge of semen other than during sex," later, "desecration, defilement" (late 14c.), from Late Latin pollutionem (nominative pollutio) "defilement," noun of action from past participle stem of Latin polluere "to soil, defile, contaminate," from por- "before" + -luere "smear," from PIE root *leu- "dirt; make dirty" (cognates: Latin lutum "mud, mire, clay," lues "filth;" Greek lyma "filth, dirt, disgrace," lymax "rubbish, refuse;" Old Irish loth "mud, dirt;" Lithuanian lutynas "pool, puddle"). Sense of "contamination of the environment" first recorded c.1860, but not common until c.1955.