1. (used in the plural) pants for casual wear
   "He changed into comfortable slacks after work"

1. The quality of being loose (not taut)
   "he hadn't counted on the slack of the rope";
   - slackness
    
2. A cord, rope or cable that is hanging loosely
   "he took up the slack"
    
3. A noticeable deterioration in performance or quality
   "a gradual slack in output";
   - slump, drop-off, falloff, falling off
    
4. A stretch of water without current or movement
   "suddenly they were in a slack and the water was motionless"; "The boats gathered in the slack water near the shore";
   - slack water
    
5. A soft wet area of low-lying land that sinks underfoot
   "The hikers carefully avoided the slack near the riverbank";
   - mire, quagmire, quag, morass
    
6. Dust consisting of a mixture of small coal fragments and coal dust and dirt that sifts out when coal is passed over a sieve
   "The miners' clothes were covered in slack after their shift"

1. Make less active or intense
   "The cool breeze slacked the oppressive humidity";
   - slake, abate
    
2. Become less in amount or intensity
   "The storm slacked off";
   - abate, let up, slack off [informal], die away
    
3. Make less active or fast
   "The runners slacked up their pace in the final mile";
   - slacken, slack up, relax
    
4. Become slow or slower
   "Business slacked during the summer months";
   - slow, slow down, slow up, slacken
    
5. Avoid responsibilities and work, be idle
   "He was caught slacking off during his shift"
    
6. Be inattentive to, or neglect
   "He slacks his attention"
    
7. Release tension on
   "slack the rope"
    
8. Cause to heat and crumble by treatment with water
   "slack lime";
   - slake

Type of: bog, come down, cord, dacks [Austral, NZ], daks [Austral, NZ], debris, declension [archaic], decline in quality, decrease, dent, deterioration, detritus, diminish, fall, fiddle, go down, goldbrick [N. Amer, informal], hydrate, junk, lessen, loose, loosen, looseness, minify, neglect, pair of trousers, pants [N. Amer], peat bog, play, rubble, shirk, sink, stretch, trousers, weaken, worsening

Encyclopedia: Slacks