"Lengthen" refers to the process of making something longer in size, duration, or extent. This can apply to various contexts, such as stretching a piece of fabric, extending a deadline, or increasing the duration of an event. The term is often used in both physical and abstract situations. In mathematics, "lengthen" can describe increasing the length of a line segment or a geometric shape. In everyday life, people might lengthen their hair through growth or styling techniques. Overall, the concept of lengthening involves the idea of expansion or extension in some form.