languor vs lassitude

languor and lassitude both are nouns.

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

As nouns, languor and lassitude are synonyms defined as:

Other synonyms of languor include listlessness.

languor (noun)	lassitude (noun)
inactivity; showing an unusual lack of energy	weakness characterized by a lack of vitality or energy
a relaxed comfortable feeling	a feeling of lack of interest or energy
a feeling of lack of interest or energy	a state of comatose torpor (as found in sleeping sickness)
oppressively still air