slack - noun

dust consisting of a mixture of small coal fragments and coal dust and dirt that sifts out when coal is passed over a sieve

a noticeable deterioration in performance or quality

a stretch of water without current or movement

a soft wet area of low-lying land that sinks underfoot

the quality of being loose (not taut)

a cord or rope or cable that is hanging loosely

slack - verb

• avoid responsibilities and work, be idle
• be inattentive to, or neglect
• release tension on
• make less active or fast
• become slow or slower
• make less active or intense
• become less in amount or intensity
• cause to heat and crumble by treatment with water

slack - adjective

• not tense or taut
• flowing with little speed as e.g. at the turning of the tide
• lacking in rigor or strictness

slack - thesaurus

abate   falloff   lax   loose   mire   morass   quag   quagmire   relax   slacken   slackness   slake   slow   slump