From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): ( n.) The part of anything that hangs loose, having no strain upon it; as, the slack of a rope or of a sail.

(2): ( adv.) Slackly; as, slack dried hops.

(3): ( superl.) Weak; not holding fast; as, a slack hand.

(4): ( n.) Small coal; also, coal dust; culm.

(5): ( n.) A valley, or small, shallow dell.

(6): ( a.) Alt. of Slacken

(7): ( superl.) Lax; not tense; not hard drawn; not firmly extended; as, a slack rope.

(8): ( v. t.) Alt. of Slacken

(9): ( superl.) Not violent, rapid, or pressing; slow; moderate; easy; as, business is slack.

(10): ( superl.) Remiss; backward; not using due diligence or care; not earnest or eager; as, slack in duty or service.

King James Dictionary [2]

Slack, a.

1. Not tense not hard drawn not firmly extended as a slack rope slack rigging slack shrouds. 2. Weak remiss not holding fast as a slack hand. 3. Remiss backward not using due diligence not earnest or eager as slack in duty or service slack in business. 4. Not violent not rapid slow as a slack pace.