A round arch that widens before rounding off WordNet 3.0 & Open English WordNet

The horseshoe arch, also called the Moorish arch and the keyhole arch, is a type of arch in which the circular curve is continued below the horizontal line of its diameter, so that the opening at the bottom of the arch is narrower than the arch's full span. Evidence for the earliest uses of this form are found in Late Antique and Sasanian architecture, but it became emblematic of Islamic architecture, especially Moorish architecture. Wikipedia

Emblematic arch common in Moorish architecture Wikidata