Noun

• S: (n) 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)
• S: (n) 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"
• S: (n) slack, slack water (a stretch of water without current or movement) "suddenly they were in a slack and the water was motionless"
• S: (n) mire, quagmire, quag, morass, slack (a soft wet area of low-lying land that sinks underfoot)
• S: (n) slack, slackness (the quality of being loose (not taut)) "he hadn't counted on the slackness of the rope"
• S: (n) slack (a cord or rope or cable that is hanging loosely) "he took up the slack"

Verb

• S: (v) slack (avoid responsibilities and work, be idle)
• S: (v) slack (be inattentive to, or neglect) "He slacks his attention"
• S: (v) slack (release tension on) "slack the rope"
• S: (v) slack, slacken, slack up, relax (make less active or fast) "He slackened his pace as he got tired"; "Don't relax your efforts now"
• S: (v) slow, slow down, slow up, slack, slacken (become slow or slower) "Production slowed"
• S: (v) slake, abate, slack (make less active or intense)
• S: (v) 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"
• S: (v) slack, slake (cause to heat and crumble by treatment with water) "slack lime"

Adjective

• S: (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"; "a slack grip"
• S: (adj) slack (flowing with little speed as e.g. at the turning of the tide) "slack water"
• S: (adj) lax, slack (lacking in rigor or strictness) "such lax and slipshod ways are no longer acceptable"; "lax in attending classes"; "slack in maintaining discipline"