Plane or Plain?

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

homesitemapA-Z confused words plane or 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.

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."