# Acute Angles (Mathematics Glossary)

# What Is an Acute Angle?

An acute angle is an angle of less than 90°.

An angle less than a right angle is an acute angle.

#### Dictionary Definition

The Oxford English Dictionary defines an acute angle as "a plane angle: less than 90 degrees."

# Real Examples of Acute Angles

The angles below are all acute angles:

##### Curriculum

##### Interactive Test

**show**

Here's a second test on acute angles.

Here's a third test on acute angles.

##### Note

# 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".

# Acute Triangles

Acute triangles are triangles that have all acute angles.

# Other Types of Angles

Acute angles are one type of angle, the other types are right, obtuse, straight, reflex and full.