Emily Dickinson Lexicon

SLACK'NESS, n.

1. Looseness; the state opposite to tension; not tightness or rigidness; as, the slackness of a cord or rope.
2. Remissness; negligence; inattention; as, the slackness of men in business or duty; slackness in the performance of engagements. – Hooker.
3. Slowness; tardiness; want of tendency; as; the slackness of flesh to heal. – Sharp.
4. Weakness; not intenseness. – Brerewood.