early 15c., "festering," from Latin sordidus "dirty, filthy, foul, vile, mean, base," from sordere "be dirty, be shabby," related to sordes "dirt, filth," from PIE *swrd-e-, from root *swordo- "black, dirty" (source also of Old English sweart "black"). Sense of "foul, low, mean" first recorded 1610s. Related: Sordidly; sordidness.