The term “triangle” comes from the Latin word “triangulum,” which means “three-cornered” or “three-angled.” This is derived from the Latin roots “tri-” meaning “three” and “angulus,” meaning “angle.”

### 1. Proto-Indo-European (PIE)

The PIE root “*trei-” means “three.”

### 2. Latin

From the PIE root, the Latin word “tri-” developed, meaning “three.” The word “angulus” means “angle” or “corner.” Combined, they form “triangulum,” meaning “three-cornered” or “three-angled.”

### 3. Old French (c. 9th to 14th century CE)

The Latin term “triangulum” evolved into Old French “triangle,” retaining the meaning of “three-cornered” or “three-angled.”

### 4. Middle English (c. 11th to 15th century CE)

The Old French “triangle” was adopted into Middle English as “triangul,” meaning “a geometric figure with three sides and three angles.”

### 5. Modern English (from 15th century CE to present)

The term “triangle” evolved into its current form and pronunciation, retaining the meaning of “a geometric figure with three sides and three angles.”

### Phonetic Evolution

Over time, the pronunciation of “triangle” has remained relatively stable from Old French to Modern English.

### Usage Examples

- “Triangle is often used to describe a geometric figure with three sides and three angles.”
- “Another example of ‘triangle’ in a sentence is ‘The students learned how to calculate the area of a triangle in math class.'”

### Cultural or Historical Notes

The development of the word “triangle” was significantly influenced by its use in geometry, architecture, and various fields of science and art. The triangle is one of the most fundamental shapes in geometry and has been studied extensively for its properties and applications.

The word “triangle” reflects the concept of a three-sided figure, emphasizing the importance of basic geometric shapes in understanding and describing the physical world. It underscores the role of triangles in various practical and theoretical contexts, including construction, engineering, and design.