torpor vs lethargy

torpor and lethargy both are nouns.

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

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

torpor: 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 torpor include hibernation, lassitude, sluggishness.

torpor (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)