planeness vs flatness

planeness and flatness both are nouns.

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

As nouns, planeness and flatness are synonyms defined as:

Other synonyms of planeness include two-dimensionality.

planeness (noun)	flatness (noun)
the property of having two dimensions	the property of having two dimensions
	inactivity; showing an unusual lack of energy
	the property of having little or no contrast; lacking highlights or gloss
	a deficiency in flavor
	a want of animation or brilliance