Palladian window

[ puh-ley-dee-uh n, -lah- ]
/ pəˈleɪ di ən, -ˈlɑ- /

noun

a window in the form of a round-headed archway with a narrower compartment on either side, the side compartments usually being capped with entablatures on which the arch of the central compartment rests.
Also called Diocletian window, Venetian window.