"of or imparting filth," early 15c. metathesis of dritty "feculent; muddy" (late 14c.), from dirt + -y (2). Sense of characterized by dirt, unclean" is from 16c. Meaning "smutty, morally unclean" is from 1590s. Of colors, from 1690s. Sense of "not streamlined; rough, untidy, or imperfect" is by 1925. Of atomic bombs, "producing much radioactive fallout," by 1956.
Dirty linen "personal or familial secrets" is first recorded 1860s. Dirty work in the figurative sense is from 1764; dirty trick is from 1670s. Dirty joke is by 1856. The dirty look someone gives you is by 1923; dirty old man "superannuated lecher" is from 1932. Related: dirtiness.
of the skin or complexion, "of a sickly color, discolored, yellowish," Middle English salu, from Old English salo "dusky, dark" (related to sol "dark, dirty"), from Proto-Germanic *salwa- (source also of Middle Dutch salu "discolored, dirty," Old High German salo "dirty gray," Old Norse sölr "dirty yellow"), from PIE root *sal- (2) "dirty, gray" (source also of Old Church Slavonic slavojocije "grayish-blue color," Russian solovoj "cream-colored"). Related: Sallowness.
originally the name of the lake, probably from Ojibwa (Algonquian) winipeg "dirty water;" compare winad "it is dirty." Etymologically related to Winnebago.
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.
In early use often hardly more emphatic than the mod. dirty; it is now a violent expression of disgust, seldom employed in polite colloquial speech. [OED]
Related: Filthily; filthiness.