early 15c., "accusation," from Late Latin detectionem (nominative detectio) "an uncovering, a revealing," noun of action from past-participle stem of detegere "uncover, expose," figuratively "discover, reveal, disclose," from de "un-, off" (see de-) + tegere "to cover," from PIE root *(s)teg- "to cover." From 1610s as "discovery, finding by search or observation," especially "act of finding out and bringing to light."
"a novel," 1765, from French roman, from Old French romanz (see romance (n.)). Roman à clef, novel in which characters represent real persons, literally "novel with a key" (French), is attested in English by 1893. And, in the days when a tec was popular reading, roman policier "a story of police detection" (1928).
Old English creopan "to move the body near or along the ground as a reptile or insect does" (class II strong verb; past tense creap, past participle cropen), from Proto-Germanic *kreupanan (source also of Old Frisian kriapa, Middle Dutch crupen, Old Norse krjupa "to creep"), perhaps from a PIE root *g(e)r- "crooked" [Watkins].
From c. 1300 as "move secretly or to evade detection," also "move slowly, feebly, or timorously." In reference to imperceptible movements of things (soil, railway rails, etc.) from 1870s. Related: Crept; creeping.
From mid-14c. with senses "lose one's footing," "slide out of place," "fall into error or fault." Sense of "pass unguarded or untaken" is from mid-15c. That of "slide, glide" is from 1520s. Transitive sense from 1510s; meaning "insert surreptitiously" is from 1680s. Related: Slipped; slipping. To slip up "make a mistake" is from 1855; to slip through the net "evade detection" is from 1902. To let (something) slip originally (1520s) was a reference to hounds on a leash; figurative use "allow to escape through carelessness" is from 1540s.
"a person who actively seeks to correct social ills in an idealistic, but usually impractical or superficial, way," 1650s (as do-good), in "Zootomia, or Observations on the Present Manners of the English: Briefly Anatomizing the Living by the Dead. With An Usefull Detection of the Mountebanks of Both Sexes," written by Richard Whitlock, a medical doctor. Probably used even then with a taint of impractical idealism. The verbal phrase do good "do good deeds" was in Old English.
Modern pejorative use seems to have begun on the socialist left, mocking those who were unwilling to take a hard line. OED has this citation, from The Nation in 1923:
There is nothing the matter with the United States except ... the parlor socialists, up-lifters, and do-goods.
The form do-gooder appears in American English by 1922, presumably because do-good was no longer felt as sufficiently noun-like. A slightly older word for this was goo-goo.
