Old English cuðe "known," past participle of cunnan (see can (v.1)), from Proto-Germanic *kunthaz (cf. Old Frisian kuth "known," Old Saxon cuth, Old High German kund, German kund, Gothic kunþs "known").
Died out as such 16c. with the emergence of could, but the old word was reborn 1896, with a new sense of "cultured, refined," as a back-formation from uncouth (q.v.). The Old English word forms the first element in the man's proper name Cuthbert, literally "famous-bright."