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See also: Slack and släck



  • IPA(key): /slæk/
  • (file)
  • Rhymes: -æk

Etymology 1[edit]

From Middle English slak, from Old English slæc (slack), from Proto-Germanic *slakaz. For sense of coal dust, compare slag.


slack (countable and uncountable, plural slacks)

  1. (uncountable) The part of anything that hangs loose, having no strain upon it.
    the slack of a rope or of a sail
  2. (countable) A tidal marsh or shallow that periodically fills and drains.
  • (small coal; coal dust): culm
  • (tidal marsh): slough
Derived terms[edit]


slack (comparative slacker, superlative slackest)

  1. Lax; not tense; not hard drawn; not firmly extended.
    a slack rope
  2. Weak; not holding fast.
    a slack hand
  3. Remiss; backward; not using due diligence or care; not earnest or eager.
    slack in duty or service
    • Bible, 2 Peter iii. 9
      The Lord is not slack concerning his promise, as some men count slackness.
  4. Not violent, rapid, or pressing.
    Business is slack.
    • 1928, Lawrence R. Bourne, chapter 3, in Well Tackled![1]:
      “They know our boats will stand up to their work,” said Willison, “and that counts for a good deal. A low estimate from us doesn't mean scamped work, but just for that we want to keep the yard busy over a slack time.”
  5. Excess; surplus to requirements.
    the slack capacity of an oil pipeline
  6. (slang, Caribbean) vulgar; sexually explicit, especially in dancehall music.
Derived terms[edit]


slack (not comparable)

  1. Slackly.
    slack dried hops

Etymology 2[edit]

From Middle English slakken, slaken, from Old English slacian, from Proto-Germanic *slakōną (to slack, slacken).


slack (third-person singular simple present slacks, present participle slacking, simple past and past participle slacked)

  1. To slacken.
    • (Can we date this quote by Robert South and provide title, author’s full name, and other details?)
      In this business of growing rich, poor men [] should slack their pace.
  2. (obsolete) To mitigate; to reduce the strength of.
    • 1590, Edmund Spenser, The Faerie Queene, III.7:
      Ne did she let dull sleepe once to relent, / Nor wearinesse to slack her hast, but fled / Ever alike [...].
  3. (followed by “off”) to procrastinate; to be lazy
  4. (followed by “off”) to refuse to exert effort
  5. To lose cohesion or solidity by a chemical combination with water; to slake.
    Lime slacks.
Derived terms[edit]

Etymology 3[edit]

Either from the adjective in Etymology 1 or the verb in Etymology 2.


slack (plural slacks)

  1. (rail transport) A temporary speed restriction where track maintenance or engineering work is being carried out at a particular place.
    • 1960 February, R. C. Riley, “The London-Birmingham services - Past, Present and Future”, in Trains Illustrated, page 103:
      A 40 m.p.h. slack at West Ruislip, quickly followed by a 30 m.p.h. slack at Gerrards Cross, increased our lateness to four minutes at High Wycombe.

Etymology 4[edit]

From Middle English slak, from Old Norse slakki (a slope). Cognate with Icelandic slakki, Norwegian slakke.


slack (plural slacks)

  1. (countable) A valley, or small, shallow dell.

Etymology 5[edit]

Probably from German Schlacke (dross, slag). Doublet of slag.


slack (uncountable)

  1. (mining) Small coal; coal dust.
    • 1905, Colliery Engineer (volume 25, page 107)
      One of the important improvements of recent years has been attained by mixing the peat pulp as it passes through the grinding machine, with other inflammable materials, such as bituminous coal dust, or slack []
    • 1959 April, P. Ransome-Wallis, “The Southern in trouble on the Kent Coast”, in Trains Illustrated, page 220:
      It had rather a woolly and uneven beat and was inclined to prime, but there was no trouble with steaming even though the tender contained mostly small slack and dust.