Semiellipse refers to a shape that appears almost oval in structure, but with flatter edges. There are several synonyms that can be used to describe this particular shape. Some of the commonly used synonyms include semi-oval, D-shaped, oblong, half-ellipse, and crescent. These synonyms help to convey the exact shape of the semiellipse in different contexts. For instance, when used in architectural designs or construction, the term D-shaped helps to describe the flatter structure of the semiellipse. Similarly, the term crescent is mainly used in astronomy to refer to the shape of the moon when it's partially illuminated. Therefore, the usage of these synonyms helps to provide an accurate and precise definition of the semiellipse shape.