## The Lesson

An acute angle is an angle of less than 90°.## Dictionary Definition

The Oxford English Dictionary defines an acute angle as "a plane angle: less than 90 degrees."## Interactive Game on the Types of Angles

## Real Examples of Acute Angles

The angles below are all acute angles:## More about Acute Angles

## What's in a Name?

Acute comes from the Latin word "acutus" meaning "sharp". An acute angle makes a sharp point.## Euclid and Acute Angles

Euclid defines angles in his book,*Elements*.

**Definition 12:**"An acute angle is an angle less than a right angle".