negligence vs slackness

negligence and slackness both are nouns.

Word	Noun	Adjective	Verb	Adverb
negligence	Yes	No	No	No
slackness	Yes	No	No	No

As nouns, slackness is a hyponym of negligence; that is, slackness is a word with a more specific, narrower meaning than negligence:

Other hyponyms of negligence include delinquency, dereliction, willful neglect, laxity, laxness, remissness.

negligence (noun)	slackness (noun)
failure to act with the prudence that a reasonable person would exercise under the same circumstances	the quality of being loose (not taut)
the trait of neglecting responsibilities and lacking concern	the quality of being lax and neglectful
	weakness characterized by a lack of vitality or energy