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.

2. To be remiss or backward; to be negligent.

3. To lose cohesion or solidity by a chemical combination with water; to slake; as, lime slacks.

4. To abate; to become less violent.

Whence these raging fires Will slacken, if his breath stir not their flames. --Milton.

5. To lose rapidity; to become more slow; as, a current of water slackens.

6. To languish; to fail; to flag.

7. To end; to cease; to desist; to slake. [Obs.]

That through your death your lineage should slack. --Chaucer.

They will not of that firste purpose slack. --Chaucer.

Source: Webster's Revised Unabridged Dictionary (1913)