|Noah Webster's Dictionary|
(n.) The quality or state of being slack.
Slackness (3 Occurrences)
2 Peter 3:9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance. (KJV ASV WBS)
Ecclesiastes 10:18 When no work is done the roof goes in, and when the hands do nothing water comes into the house. (See NAS)
Jeremiah 48:10 Cursed be he that doeth the work of the LORD with a slack hand, and cursed be he that keepeth back his sword from blood. (See RSV)