phlegm vs inactiveness

phlegm and inactiveness both are nouns.

Word	Noun	Adjective	Verb	Adverb
phlegm	Yes	No	No	No
inactiveness	Yes	No	No	No

As nouns, inactiveness is a hypernym of phlegm; that is, inactiveness is a word with a broader meaning than phlegm:

Other hypernyms of phlegm include inactivity, inertia.

phlegm (noun)	inactiveness (noun)
inactivity; showing an unusual lack of energy	a disposition to remain inactive or inert
expectorated matter; saliva mixed with discharges from the respiratory passages; in ancient and medieval physiology it was believed to cause sluggishness	the state of being inactive
apathy demonstrated by an absence of emotional reactions