1. (noun)slack 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. (noun)slump, slack, drop-off, falloff, falling off a noticeable deterioration in performance or quality "the team went into a slump"; "a gradual slack in output"; "a drop-off in attendance"; "a falloff in quality"
3. (noun)slack, slack water a stretch of water without current or movement "suddenly they were in a slack and the water was motionless"
4. (noun)mire, quagmire, quag, morass, slack a soft wet area of low-lying land that sinks underfoot
5. (noun)slack, slackness the quality of being loose (not taut) "he hadn't counted on the slackness of the rope"
6. (adj)slack a cord or rope or cable that is hanging loosely "he took up the slack"
7. (adj)loose, slack not tense or taut "the old man's skin hung loose and grey"; "slack and wrinkled skin"; "slack sails"; "a slack rope"
8. (adj)slack flowing with little speed as e.g. at the turning of the tide "slack water"
9. (verb)lax, slack lacking in rigor or strictness "such lax and slipshod ways are no longer acceptable"; "lax in attending classes"; "slack in maintaining discipline"
10. (verb)slack avoid responsibilities and work, be idle
11. (verb)slack be inattentive to, or neglect "He slacks his attention"
12. (verb)slack release tension on "slack the rope"
13. (verb)slack, slacken, slack up, relax make less active or fast "He slackened his pace as he got tired"; "Don't relax your efforts now"
14. (verb)slow, slow down, slow up, slack, slacken become slow or slower "Production slowed"
15. (verb)slake, abate, slack make less active or intense
16. (verb)abate, let up, slack off, slack, die away become less in amount or intensity "The storm abated"; "The rain let up after a few hours"
17. (verb)slack, slake cause to heat and crumble by treatment with water "slack lime"
Definitions of 'slack'
Webster 1913 Dictionary
1. (adj)slack alt. of Slacken
2. (adverb)slack slackly; as, slack dried hops
3. (noun)slack small coal; also, coal dust; culm
4. (noun)slack a valley, or small, shallow dell
5. (noun)slack the part of anything that hangs loose, having no strain upon it; as, the slack of a rope or of a sail
6. slack lax; not tense; not hard drawn; not firmly extended; as, a slack rope
7. slack weak; not holding fast; as, a slack hand
8. slack remiss; backward; not using due diligence or care; not earnest or eager; as, slack in duty or service
9. slack not violent, rapid, or pressing; slow; moderate; easy; as, business is slack
Definition of slack 
