languor vs flatness

languor and flatness both are nouns.

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

As nouns, languor and flatness are synonyms defined as:

Other synonyms of languor include lethargy, phlegm, sluggishness.

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