sluggishness vs sluggish

sluggishness is a noun but sluggish is not a noun.

Word	Noun	Adjective	Verb	Adverb
sluggishness	Yes	No	No	No
sluggish	No	Yes	No	No

sluggishness (noun)	sluggish (noun)
inactivity; showing an unusual lack of energy
the pace of things that move relatively slowly
a state of comatose torpor (as found in sleeping sickness)

sluggishness (adjective)	sluggish (adjective)
	slow and apathetic
	(of business) not active or brisk
	slow or slothful