Source : Webster's Revised Unabridged Dictionary (1913)

Slack \Slack\, Slacken \Slack"en\, v. t.
   1. To render slack; to make less tense or firm; as, to slack
      a rope; to slacken a bandage. --Wycklif (Acts xxvii. 40)

   2. To neglect; to be remiss in. [Obs.] --Shak.

            Slack not the pressage.               --Dryden.

   3. To deprive of cohesion by combining chemically with water;
      to slake; as, to slack lime.

   4. To cause to become less eager; to repress; to make slow or
      less rapid; to retard; as, to slacken pursuit; to slacken
      industry. ``Rancor for to slack.'' --Chaucer.

            I should be grieved, young prince, to think my
            presence Unbent your thoughts, and slackened 'em to
            arms.                                 --Addison.

            In this business of growing rich, poor men should
            slack their pace.                     --South.

            With such delay Well plased, they slack their
            course.                               --Milton.

   5. To cause to become less intense; to mitigate; to abate; to
      ease.

            To respite, or deceive, or slack thy pain Of this
            ill mansion.                          --Milton.

   {Air-slacked lime}, lime slacked by exposure to the air, in
      consequence of the absorption of carton dioxide and water,
      by which it is converted into carbonate of lime and
      hydrate of lime.