couth

From Middle English couth (“familiar, known; evident, true; famous, respected, well-known; genteel, having good manners”), from Old English cūþ (“familiar, intimate, known, usual; certain, plain, manifest; famous, noted, well-known; excellent; friendly; related”), past participle of cunnan (“to be familiar with, know; can, to be able, know how”), from Proto-Germanic *kunnaną (“to be familiar with, know, recognize; to be able, know how”) (compare *kunþaz (“known”)), ultimately from Proto-Indo-European *ǵneh₃- (“to know”). The word is cognate with Dutch kond (“known”), Saterland Frisian cut (“known”), Gothic 𐌺𐌿𐌽𐌸𐍃 (kunþs, “known”), Icelandic kuður, kunnur (“known”), Latin gnosco (“to know”), Old High German kund, chund, chunt, Middle High German kunt (modern German kund (“known”)), Old Saxon kūth, cûth, cuð (“known; famous, renowned”), Scots couth (“familiar, known”); and is a doublet of could.

Back-formation from uncouth.