torpidity vs lethargy

torpidity and lethargy both are nouns.

Word	Noun	Adjective	Verb	Adverb
torpidity	Yes	No	No	No
lethargy	Yes	No	No	No

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

torpidity: a state of motor and mental inactivity with a partial suspension of sensibility
lethargy: a state of comatose torpor (as found in sleeping sickness)

Other hyponyms of torpidity include hibernation, lassitude, sluggishness.

torpidity (noun)	lethargy (noun)
inactivity resulting from lethargy and lack of vigor or energy	weakness characterized by a lack of vitality or energy
a state of motor and mental inactivity with a partial suspension of sensibility	inactivity; showing an unusual lack of energy
	a state of comatose torpor (as found in sleeping sickness)