Incurvity is a rarely used word that refers to the state of being curved or bent inwards. There are several synonyms for incurvity, including concavity, indentation, curvature, arch, arc, bow, crook, curl, bend, flexure, and curve. These words are often used when describing the shape of objects, such as the arc of a rainbow or the curvature of a horseshoe. They can also be used to describe physical features, like the curl of a person's hair or the bow of their lips. While incurvity may not be a commonly used word, its synonyms can be used to add detail and specificity to descriptions in both written and spoken language.