flatness vs languor

flatness and languor both are nouns.

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

As nouns, flatness and languor are synonyms defined as:

Other synonyms of flatness include lethargy, phlegm, sluggishness.

flatness (noun)	languor (noun)
the property of having two dimensions	inactivity; showing an unusual lack of energy
inactivity; showing an unusual lack of energy	a relaxed comfortable feeling
the property of having little or no contrast; lacking highlights or gloss	a feeling of lack of interest or energy
a deficiency in flavor	oppressively still air
a want of animation or brilliance