1) Type of arch 
The horseshoe arch, also called the Moorish arch and the Keyhole arch, is the emblematic arch of Islamic architecture. They were formerly constructed in Visigothic Spain. Horseshoe arches can take rounded, pointed or lobed form. Horseshoe arches are known from pre-Islamic Syria where the form was used in the fourth century CE in the Baptistery of ...
* Arch.
Arch in which the bottom is smaller than the mid-span; found in Moorish architecture 
An arch shaped like a horseshoe. It is found particularly in Spain or in buildings influenced by Spanish ones. 
An arch shaped like a horseshoe. Although seen to be associated with Islamic architecture, this form of arch actually predates it. Horseshoe arches are common in Armenian churches that predate the Arab conquests.
an arch with the intrados widening above the springing and then narrowing to a rounded crown. Also calledSee illus. under