PLAIN is an adverb which means, simple and ordinary looking, with no decorations.
It is also used as an adverb to emphasize upon something
As a noun, Plain is also used to define a large flat area, with fewer trees
Sentences:
- She is wearing a plain dress.
- I mean, you took the wrong way home, that’s plain stupid.
- High mountains rise above the plain.
PLANE is a noun, commonly used to describe an airplane.
In mathematical terms, it is used to define a flat surface where a straight line joining two points can wholly lie.
Sentences:
- The plane is flying high, above the sky.
- Two planes intersect each other in a three-dimensional surface
