n.

1. dust consisting of a mixture of small coal fragments and coal dust and dirt that sifts out when coal is passed over a sieve
2. a noticeable deterioration in performance or quality;
   slump, drop-off, falloff, falling off
   
   • the team went into a slump
   • a gradual slack in output
   • a drop-off in attendance
   • a falloff in quality
3. a stretch of water without current or movement;
   slack water
   
   • suddenly they were in a slack and the water was motionless
4. a soft wet area of low-lying land that sinks underfoot;
   mire, quagmire, quag, morass
5. the condition of being loose (not taut);
   slackness
   
   • he hadn't counted on the slackness of the rope
6. a cord or rope or cable that is hanging loosely
   
   • he took up the slack

v.

1. avoid responsibilities and work, be idle
2. be inattentive to, or neglect
   
   • He slacks his attention
3. release tension on
   
   • slack the rope
4. make less active or fast;
   slacken, slack up, relax
   
   • He slackened his pace as he got tired
   • Don't relax your efforts now
5. become slow or slower;
   slow, slow down, slow up, slacken
   
   • Production slowed
6. make less active or intense;
   slake, abate
7. become less in amount or intensity;
   abate, let up, slack off, die away
   
   • The storm abated
   • The rain let up after a few hours
8. cause to heat and crumble by treatment with water;
   slake
   
   • slack lime

adj.

1. not tense or taut;
   loose
   
   • the old man's skin hung loose and grey
   • slack and wrinkled skin
   • slack sails
   • a slack rope
2. lacking in strength or firmness or resilience;
   flaccid, lax, limp
   
   • flaccid muscles
   • took his lax hand in hers
   • gave a limp handshake
   • a limp gesture as if waving away all desire to know" G.K.Chesterton; "a slack grip
3. flowing with little speed as e.g. at the turning of the tide
   
   • slack water
4. lacking in rigor or strictness;
   lax
   
   • such lax and slipshod ways are no longer acceptable
   • lax in attending classes
   • slack in maintaining discipline