flatness vs planeness

flatness and planeness both are nouns.

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

As nouns, flatness and planeness are synonyms defined as:

Other synonyms of flatness include two-dimensionality.

flatness (noun)	planeness (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