Definition of Slack

Adjective: slack (slacker,slackest) slak

Not tense or taut
"slack and wrinkled skin"; "slack sails"; "a slack rope";
- loose
Flowing with little speed as e.g. at the turning of the tide
"slack water"
Lacking in rigour or strictness
"slack in maintaining discipline";
- lax

Noun: slack slak

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 gradual slack in output";
- slump, drop-off, falloff, falling off
A stretch of water without current or movement
"suddenly they were in a slack and the water was motionless";
- slack water
A soft wet area of low-lying land that sinks underfoot
- mire, quagmire, quag, morass
The quality of being loose (not taut)
"he hadn't counted on the slack of the rope";
- slackness
A cord, rope or cable that is hanging loosely
"he took up the slack"

Verb: slack slak

Avoid responsibilities and work, be idle
Be inattentive to, or neglect
"He slacks his attention"
Release tension on
"slack the rope"
Make less active or fast
"He slacked his pace as he got tired";
- slacken, slack up, relax
Become slow or slower
- slow, slow down, slow up, slacken
Make less active or intense
- slake, abate
Become less in amount or intensity
"The storm slacked off";
- abate, let up, slack off, die away
Cause to heat and crumble by treatment with water
"slack lime";
- slake