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.
plane or plain?

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.


The word "plain" has three main meanings:

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

  • a plain girl correct tick
  • a plain cake correct tick
  • a plain colour correct tick

(2) Apparent

  • It is plain to see. correct tick
  • It seems quite plain to me. correct tick
Plain is an adjective in these examples.

(3) An expanse of level and low land

  • The Russian Plain. correct tick
  • I joined the Chinese farmers as they attempted to drive the yaks across the plain in western China. correct tick
Plain is a noun in these examples.


The word "plane" has six main meanings:

(1) An airplane

  • What time is your plane? correct tick
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. correct tick

(3) A level (usually figurative)

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

(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? correct tick

(6) To travel on the surface of water

  • The car hit the puddle and planed straight into the back of the lorry. correct tick
  • (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 an airplane.

Therefore, if it's above the ground, it's almost certainly "plane."
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This page was written by Craig Shrives.