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See more synonyms for slack on Thesaurus.com
  1. not tight, taut, firm, or tense; loose: a slack rope.
  2. negligent; careless; remiss: slack proofreading.
  3. slow, sluggish, or indolent: He is slack in answering letters.
  4. not active or busy; dull; not brisk: the slack season in an industry.
  5. moving very slowly, as the tide, wind, or water.
  6. weak; lax.
  7. Nautical. easy(def 15a).
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  1. in a slack manner.
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  1. a slack condition or part.
  2. the part of a rope, sail, or the like, that hangs loose, without strain upon it.
  3. a decrease in activity, as in business or work: a sudden slack in output.
  4. a period of decreased activity.
  5. Geography. a cessation in a strong flow, as of a current at its turn.
  6. a depression between hills, in a hillside, or in the land surface.
  7. Prosody. (in sprung rhythm) the unaccented syllable or syllables.
  8. British Dialect. a morass; marshy ground; a hollow or dell with soft, wet ground at the bottom.
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verb (used with object)
  1. to be remiss in respect to (some matter, duty, right, etc.); shirk; leave undone: He slacked the most important part.
  2. to make or allow to become less active, vigorous, intense, etc.; relax (efforts, labor, speed, etc.); lessen; moderate (often followed by up).
  3. to make loose, or less tense or taut, as a rope; loosen (often followed by off or out).
  4. to slake (lime).
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verb (used without object)
  1. to be remiss; shirk one's duty or part.
  2. to become less active, vigorous, rapid, etc. (often followed by up): Business is slacking up.
  3. to become less tense or taut, as a rope; to ease off.
  4. to become slaked, as lime.
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  1. take up the slack,
    1. to pull in or make taut a loose section of a rope, line, wire, etc.: Take up the slack before releasing the kite.
    2. to provide or compensate for something that is missing or incomplete: New sources of oil will take up the slack resulting from the embargo.
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Origin of slack

before 900; Middle English slac (adj.), Old English sleac, slæc; cognate with Old Norse slakr, Old High German slach, Latin laxus lax
Related formsslack·ing·ly, adverbslack·ly, adverbslack·ness, nounun·slacked, adjectiveun·slack·ing, adjective

Synonyms for slack

See more synonyms for on Thesaurus.com
1. relaxed. 2. lazy, weak. 3. dilatory, tardy, late. 4. idle, quiet. 11. slowing, relaxation. 17. neglect. 18. reduce, slacken. 21. malinger.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for slack off

breathe, relax, lean, dim, abate, ebb, dwindle, subside, atrophy, wither, decrease, fade, slacken, shrink, weaken, wane, reduce, soften, curb, decline

British Dictionary definitions for slack off


  1. not tight, tense, or taut
  2. negligent or careless
  3. (esp of water, etc) moving slowly
  4. (of trade, etc) not busy
  5. phonetics another term for lax (def. 4)
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  1. in a slack manner
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  1. a part of a rope, etc, that is slacktake in the slack
  2. a period of decreased activity
    1. a patch of water without current
    2. a slackening of a current
  3. prosody (in sprung rhythm) the unstressed syllable or syllables
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  1. to neglect (one's duty, etc)
  2. (often foll by off) to loosen; to make slack
  3. chem a less common word for slake (def. 3)
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See also slacks
Derived Formsslackly, adverbslackness, noun

Word Origin for slack

Old English slæc, sleac; related to Old High German slah, Old Norse slākr bad, Latin laxus lax


  1. small pieces of coal with a high ash content
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Word Origin for slack

C15: probably from Middle Low German slecke; related to Dutch slak, German Schlacke dross
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for slack off



Old English slæc "remiss, lax, characterized by lack of energy, sluggish, indolent, languid; slow, gentle, easy," from Proto-Germanic *slakas (cf. Old Saxon slak, Old Norse slakr, Old High German slah "slack," Middle Dutch lac "fault, lack"), from PIE root *(s)leg- "to be slack" (see lax).

Sense of "not tight" (in reference to things) is first recorded c.1300. As an adverb from late 14c. Slack-key (1975) translates Hawaiian ki ho'alu. Slack water (n.) "time when tide is not flowing" is from 1769. Slack-handed "remiss" is from 1670s. Slack-baked "baked imperfectly, half-baked" is from 1823; figuratively from 1840.

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"coal dust," mid-15c., sleck, of uncertain origin, probably related to Middle Dutch slacke, Middle Low German slecke "slag, small pieces left after coal is screened," perhaps related to slagge "splinter flying off metal when it is struck" (see slag (n.)).

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early 14c., "cessation" (of pain, grief, etc.), from slack (adj.). Meaning "a cessation of flow in a current or tide" is from 1756; that of "still stretch of a river" is from 1825. Meaning "loose part or end" (of a rope, sail, etc.) is from 1794; hence figurative senses in take up the slack (1930 figuratively) and slang cut (someone) some slack (1968). Meaning "quiet period, lull" is from 1851. Slacks "loose trousers" first recorded 1824, originally military.

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1510s, "to moderate, make slack," back-formed from slack (adj.) after the original verb veered into the specialized sense of slake. Meaning "be remiss, inactive or idle, fail to exert oneself" is attested from 1540s; current use is probably a re-coining from c.1904 (see slacker, and cf. Old English slacful "lazy," sleacmodnes "laziness"). Related: Slacked; slacking.

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Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with slack off

slack off

Decrease in activity or intensity, as in If business ever slacks off we can go on vacation, or When the project fell behind schedule again, she thought we were slacking off. [Second half of 1800s]

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.