Plane or Plain?

What Is the Difference between "Plane" and "Plain"?

"Plane" and "plain" are easy to confuse because they sound identical (i.e., they are perfect homonyms). However, their meanings are very different.

• "Plane" usually means an airplane, a flat surface, or a tool for shaving wood.
• "Plain" usually means simple or an expanse of lowland.

More about "Plane" and "Plain"

The words "plane" and "plain" have several meanings. Unfortunately, both have a meaning relating to flatness, and this is often the source of confusion.

Plain

The word "plain" has three main meanings:

(1) Simple (i.e., not elaborate)

• a plain girl
• a plain cake
• a plain colour

(2) Apparent

• It is plain to see.
• It seems quite plain to me.

Plain is an adjective in these examples.

(3) An expanse of level and low land

• The Russian Plain.
• I joined the Chinese farmers as they attempted to drive the yaks across the plain in western China.

Plain is a noun in these examples.

Plane

The word "plane" has six main meanings:

(1) An airplane

• What time is your plane?

Do you say "airplane" or "aeroplane"?

(2) A flat surface (especially in mathematics)

• In a 3D space, a plane can be defined by specifying a point and a normal vector to the plane.

(3) A level (usually figurative)

• I was hoping for a conversion on a higher plane.

(4) A tool for smoothing or shaping wood (i.e., a carpenter's plane)

(5) To shave wood into shape

• Can you plane a few inches off the top of the door?

(6) To travel on the surface of water

• The car hit the puddle and planed straight into the back of the lorry.
(This is also known as "to aquaplane.")

Planes Are above Ground

Confusion arises mostly between "plain" meaning expanse of lowland and "plane" meaning a flat surface or a level.

A plain (lowland) is always on the ground. A plane (a surface or a level) is nearly always above the ground...like an airplane.

Therefore, if it's above the ground, it's almost certainly "plane."