nonplanar

As adjectives the difference between nonplanar and flat

is that nonplanar is not planar while flat is having no variations in height.

As an adverb flat is

so as to be flat.

As a noun flat is

an area of level ground or flat can be (archaic|new england|now chiefly british) an apartment.

As a verb flat is

(poker slang) to make a flat call; to call without.

As adjectives the difference between nonplanar and nonplantar

is that nonplanar is not planar while nonplantar is not plantar.

As an adjective nonplanar

is not planar.

As a noun nonplanarity is

the property of being nonplanar.