The ability to speak three languages.

A shape with three sides and three corners.

A stand with three legs, often used to hold a camera.

Having three colors. 

Involving three sides or groups. 

If you are afraid of spiders, you suffer from this.

When the body's immune system attacks itself.

Behavior that goes against social norms or avoids social interaction.

A group of related words that share a common base or root.

A branch of science that weather reporters must study.