Origin and history of know-nothing

Old English cnawan (class VII strong verb; past tense cneow, past participle cnawen), "perceive a thing to be identical with another," also "be able to distinguish" generally (tocnawan); "perceive or understand as a fact or truth" (opposed to believe); "know how (to do something)," from Proto-Germanic *knew- (source also of Old High German bi-chnaan, ir-chnaan "to know"), from PIE root *gno- "to know."

For pronunciation, see kn-. Once widespread in Germanic, the verb is now retained there only in English, where it has widespread application, covering meanings that require two or more verbs in other languages (such as German wissen, kennen, erkennen and in part können; French connaître "perceive, understand, recognize," savoir "have a knowledge of, know how;" Latin scire "to understand, perceive," cognoscere "get to know, recognize;" Old Church Slavonic znaja, vemi). The Anglo-Saxons also used two distinct words for this, the other being witan (see wit (v.)).

From c. 1200 as "to experience, live through." The meaning "to have sexual intercourse with," also found in other modern languages, is attested from c. 1200, from the Old Testament (Genesis iv.1). Attested from 1540s in colloquial phrases suggesting cunning or savvy (but often in the negative).

As far as (one) knows "to the best of (one's) knowledge" is late 14c. Expression God knows is from c. 1400. To know too much (to be allowed to live, escape, etc.) is from 1872. To know better "to have learned from experience" is from 1704.

As an expression of surprise, what do you know attested by 1914. Don't I know it in the opposite sense ("you need not tell me") is by 1841.

"no thing, not any thing, not something," Middle English, from Old English naþing, naðinc, from nan "not one" (see none) + þing "thing" (see thing). Meaning "insignificant thing, thing of no consequence" is from c. 1600. As an adverb, "not at all, in no degree," late Old English. As an adjective by 1961. For nothing "not at all" is from c. 1300. Nothing to it, indicating something easy to do, is by 1925. Nothing to write home about, indicating an unremarkable circumstance or thing, is from 1917 among the World War I soldiers.