"Half a circle" can be described using a variety of synonyms, depending on the context and intended meaning. One such synonym is "semicircle," which is often used in mathematics and geometry to refer to a shape that is exactly half of a circle. Another possible synonym is "arc," which can be used to describe any curved segment of a circle or other circular shape. Other synonyms for "half a circle" might include phrases like "180-degree arc," "half-moon shape," or "curve of a half-circle." These synonyms can be useful for adding variety and specificity to descriptions of circular shapes and their components.