loose vs slack

loose is not a noun while slack is a noun.

Word	Noun	Adjective	Verb	Adverb
loose	No	Yes	Yes	Yes
slack	Yes	Yes	Yes	No

As adjectives, loose and slack are synonyms defined as:

As verbs, slack is a hyponym of loose; that is, slack is a word with a more specific, narrower meaning than loose:

Other hyponyms of loose include relax, unbend, remit, slacken, unscrew, unscrew.

loose (noun)	slack (noun)
	a cord or rope or cable that is hanging loosely
	the quality of being loose (not taut)
	a stretch of water without current or movement
	a soft wet area of low-lying land that sinks underfoot
	a noticeable deterioration in performance or quality
	dust consisting of a mixture of small coal fragments and coal dust and dirt that sifts out when coal is passed over a sieve

loose (adjective)	slack (adjective)
not tight; not closely constrained or constricted or constricting	not tense or taut
not compact or dense in structure or arrangement	lacking in rigor or strictness
not affixed	flowing with little speed as e.g. at the turning of the tide
(of textures) full of small openings or gaps
not literal
lacking a sense of restraint or responsibility
not tense or taut
casual and unrestrained in sexual behavior
emptying easily or excessively
(of a ball in sport) not in the possession or control of any player
not officially recognized or controlled
not carefully arranged in a package
having escaped, especially from confinement

loose (verb)	slack (verb)
become loose or looser or less tight	release tension on
make loose or looser	make less active or fast
turn loose or free from restraint	make less active or intense
grant freedom to; free from confinement	become slow or slower
	cause to heat and crumble by treatment with water
	become less in amount or intensity
	be inattentive to, or neglect
	avoid responsibilities and work, be idle

loose (adverb)	slack (adverb)
without restraint