1. The quality of being loose (not taut)
   "he hadn't counted on the slackness of the rope";
   - slack
    
2. The quality of being lax and neglectful
   "The security guard's slackness in checking IDs allowed unauthorized access to the building";
   - laxness, laxity, remissness
    
3. Weakness characterized by a lack of vitality or energy
   "The heat wave caused a general slackness among the workers";
   - inanition, lassitude, lethargy

Type of: looseness, neglect, neglectfulness, negligence, play, weakness

Encyclopedia: Slackness