1. becomes less tight, tense, or firm
2. becomes slower or less active
3. makes something less tight, tense, or firm

Examples

• The rope slackens as the weight is removed.
• Her grip slackens when she falls asleep.
• Business activity slackens during the summer months.
• The teacher slackens the rules on the last day of school.
• He slackens his pace as he approaches the finish line.
• The wind slackens in the evening.
• She slackens the tension in the guitar strings.