Concave vs. Convex

Although the two words concave and convex look similar, they have opposite meanings.

An object that is concave has a surface that curves inward. Meanwhile, an object that is convex has a surface that protrudes outward.

The front side of a spoon is concave because it curves inward, while the back of the spoon is convex because it curves outward.

Another everyday object that can be concave or convex is a mirror. Concave mirrors are used by people doing makeup so they could have a zoomed in view of their face while applying their products.

Large convex mirrors are placed at streets with sharp turns for drivers to have a wide view of the other side of the road.

Let us break down the Latin root of the two words.

For the word concave, the con- means with in Latin, and the cave comes from the Latin word cavus, which means hollow or hole. The Latin root of the word explain why the word concave is used to describe surfaces that curve inward; the hollow part of the inward-facing surface is the cave part of the word.

The word convex comes from the Latin word convexus, which means arched or vaulted. That explains why the word is being used to describe a surface that curves outward like an arch.

In the above image, you can see that the leftmost shape is convex on both sides, hence the name biconvex, the suffix bi- meaning twice or on both sides.

Meanwhile, the rightmost shape is concave on both sides, resulting in the name biconcave, which means it is curved inward on both sides.

Here is a small quiz. Do you think these following are concave or convex? The answers are at the end of the page.

The inside of a bowl
A magnifying glass’s lens that curves outward on both sides
The top of a domed stadium
The surface of an orb
The inner side of glasses for nearsightedness that curve inward

Let us take at a look at some example sentences to see how each word is used in context.

The nomad made a concave shape with his hands to scoop up and drink the water from the river.

The nomad in this sentence is making a cup with his hands to easily drink water. The inward curving shape helps retain the water until it reaches his mouth.