To become slack.To become less active; fall off: as, trade slackened; the demand slackens; prices slackenTo become remiss or neglectful, as of duty.To make slack or slacker.To abate; moderate; lessen; diminish the intensity, severity, rate, etc., of; hence, to mitigate; assuage; relieve: as, to slacken one's pace; to slacken cares.To be or become remiss in or neglectful of; remit; relax: as, to slacken labor or exertion.n. The slags or cinder from previous fusions, used in smelting operations to mix with natural ores and to retard fusion of the ores until reduction shall have proceeded to the desired point.