Sinus Meridianii
[ see-nuh s muh-rid-ee-ah-nee-ee, sahy-nuh s muh-rid-ee-ey-nee-ahy ]
/ ˈsi nəs məˌrɪd iˈɑ niˌi, ˈsaɪ nəs məˌrɪd iˈeɪ niˌaɪ /
noun
an area on the equator of Mars, appearing as a dark region when viewed telescopically from the earth.