sluggishness vs lassitude

sluggishness and lassitude both are nouns.

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

As nouns, sluggishness and lassitude are synonyms defined as:

sluggishness and lassitude: a state of comatose torpor (as found in sleeping sickness)

Other synonyms of sluggishness include lethargy.

sluggishness (noun)	lassitude (noun)
inactivity; showing an unusual lack of energy	weakness characterized by a lack of vitality or energy
the pace of things that move relatively slowly	a feeling of lack of interest or energy
a state of comatose torpor (as found in sleeping sickness)	a state of comatose torpor (as found in sleeping sickness)