Sinus Iridum

[ see-nuh s ir-i-duh m, sahy- ]
/ ˈsi nəs ˈɪr ɪ dəm, ˈsaɪ- /

noun

(Bay of Rainbows) a semicircular dark plain in the second quadrant of the face of the moon.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019