Demi-lune is a French term that means "half-moon." It refers to a crescent-shaped object or structure, such as a fortification or a piece of furniture. There are a variety of synonyms for demi-lune, depending on the context in which it is used. Some possible alternatives include "crescent," "semicircle," "half circle," "arc," "bowed," and "curved." These synonyms can be used in different ways, depending on the intended meaning and tone of the sentence. For example, "crescent" might be used to describe the shape of a lunar eclipse, while "curved" could be used to describe the body of a sleek sports car.