Triangular (adjective)

1. Having three sides and three angles.
2. Having a shape or form that is triangular.
3. Having the form of a triangle.

Origin:

Mid 17th century: from latin triangularis, from triangulum "triangle".

Examples:

1. The triangular pyramid had three sides and three angles.
2. The triangular sail caught the wind and propelled the boat forward.
3. The triangular-shaped building had a unique and modern design.
4. The triangular piece of cloth was folded into a distinctive headscarf.
5. The triangular pattern of the wallpaper added interest to the otherwise plain room.