"mass of slag," 1769, from klincard (1640s), a type of paving brick made in Holland, from Dutch klinkaerd, from klinken "to ring" (as it does when struck), of imitative origin. Also "a clinch-nail;" hence clinker-built (1769). The meaning "stupid mistake" is first recorded 1950 in American English; originally (1942) "a wrong note in music."