1. in a loose, not tight manner
2. in a careless or lazy manner; without proper effort or attention

Examples

• The rope hung slackly from the tree branch.
• Her jaw dropped slackly in surprise.
• The student slackly completed his homework without checking for errors.
• The security guard slackly monitored the entrance.
• The sail hung slackly in the still air.
• She slackly performed her duties, missing several important details.