looseness vs slackness

looseness and slackness both are nouns.

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

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

Other hyponyms of looseness include wiggliness, slack.

looseness (noun)	slackness (noun)
dissolute indulgence in sensual pleasure	the quality of being loose (not taut)
movement or space for movement	the quality of being lax and neglectful
a lack of strict accuracy; laxity of practice	weakness characterized by a lack of vitality or energy
freedom from restraint
the quality of movability by virtue of being free from attachment or other restraints
frequent and watery bowel movements; can be a symptom of infection or food poisoning or colitis or a gastrointestinal tumor