A spongy, semivitrifled substance which miners or smelters mix with the ores of metals to prevent their fusion.
- To make or become slower; slow down: The runners slackened their pace. Air speed slackened.
- To make or become less tense, taut, or firm; loosen: I slackened the line to let the fish swim. The tension in the board room finally slackened.
- To make or become less vigorous, intense, or severe; ease: slacken discipline; afraid that morale might slacken.