"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.
Old English word "speech, talk, utterance, sentence, statement, news, report, word," from Proto-Germanic *wurda- (source also of Old Saxon, Old Frisian word, Dutch woord, Old High German, German wort, Old Norse orð, Gothic waurd), from PIE *were- (3) "speak, say" (see verb).
The meaning "promise" was in Old English, as was the theological sense. In the plural, the meaning "verbal altercation" (as in have words with someone) dates from mid-15c. Word-processor first recorded 1971; word-processing is from 1972; word-wrap is from 1977. A word to the wise is from Latin phrase verbum sapienti satis est "a word to the wise is enough." Word-for-word "in the exact word or terms" is late 14c. Word of mouth "spoken words, oral communication" (as distinguished from written words) is by 1550s.
It is dangerous to leave written that which is badly written. A chance word, upon paper, may destroy the world. Watch carefully and erase, while the power is still yours, I say to myself, for all that is put down, once it escapes, may rot its way into a thousand minds, the corn become a black smut, and all libraries, of necessity, be burned to the ground as a consequence. [William Carlos Williams, "Paterson"]
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.