not tight, taut, firm, or tense; loose

a slack rope.

negligent; careless; remiss

slack proofreading.

slow, sluggish, or indolent

He is slack in answering letters.

not active or busy; dull; not brisk

the slack season in an industry.

moving very slowly, as the tide, wind, or water.

weak; lax.

Nautical . easy ( def. 15a ) .

in a slack manner.

a slack condition or part.

the part of a rope, sail, or the like, that hangs loose, without strain upon it.

a decrease in activity, as in business or work

a sudden slack in output.

a period of decreased activity.

Geography . a cessation in a strong flow, as of a current at its turn.

a depression between hills, in a hillside, or in the land surface.

Prosody . (in sprung rhythm) the unaccented syllable or syllables.

British Dialect . a morass; marshy ground; a hollow or dell with soft, wet ground at the bottom.

to be remiss in respect to (some matter, duty, right, etc.); shirk; leave undone

He slacked the most important part.

to make or allow to become less active, vigorous, intense, etc.; relax (efforts, labor, speed, etc.); lessen; moderate (often fol. by up ).

to make loose, or less tense or taut, as a rope; loosen (often fol. by off or out ).

to slake (lime).

to be remiss; shirk one's duty or part.

to become less active, vigorous, rapid, etc. (often fol. by up )

Business is slacking up.

to become less tense or taut, as a rope; to ease off.

to become slaked, as lime. ?

take up the slack

to pull in or make taut a loose section of a rope, line, wire, etc.

Take up the slack before releasing the kite.

to provide or compensate for something that is missing or incomplete

New sources of oil will take up the slack resulting from the embargo.

adjective

rigid , stiff , taut , tight , active , alert , disciplined

noun

rigidity , stiffness , tautness , tightness

adjective

dull , easy , feeble , flabby , flaccid , flexible , flimsy , inert , infirm , laggard , lax , leisurely , limp , not taut , passive , quaggy , quiet , relaxed , sloppy , slow , slow-moving , sluggish , soft , supine , unsteady , weak , asleep on the job , behindhand , careless , delinquent , derelict , dilatory , disregardful , dormant , easy-going , faineant , idle , inactive , inattentive , indolent , lackadaisical , lethargic , neglectful , not busy , permissive , quiescent , regardless , remiss , slothful , stagnant , tardy , down , off

noun

give , leeway , play , room , slackening , slowdown , slow-up

verb

let up , loose , loosen , relax , slacken , untighten , disregard , shirk

phrasal verb

abate , bate , die , ease , ebb , fall , fall off , lapse , let up , moderate , remit , slacken , wane