from
The Collaborative International Dictionary of English v.0.48
Slack \Slack\, Slacken \Slack"en\, v. i. [imp. & p. p.
{Slacked}, {Slackened}; p. pr. & vb. n. {Slacking},
{Slackening}.] [See {Slack}, a.]
1. To become slack; to be made less tense, firm, or rigid; to
decrease in tension; as, a wet cord slackens in dry
weather.
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2. To be remiss or backward; to be negligent.
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3. To lose cohesion or solidity by a chemical combination
with water; to slake; as, lime slacks.
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4. To abate; to become less violent.
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Whence these raging fires
Will slacken, if his breath stir not their flames.
--Milton.
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5. To lose rapidity; to become more slow; as, a current of
water slackens.
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6. To languish; to fail; to flag.
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7. To end; to cease; to desist; to slake. [Obs.]
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That through your death your lineage should slack.
--Chaucer.
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They will not of that firste purpose slack.
--Chaucer.
[1913 Webster] Slack