Sinus Iridum
[
see
-n
uh
s
ir
-i-d
uh
m,
sahy
-]
/ˈsi nəs ˈɪr ɪ dəm, ˈsaɪ-/
noun
1.
(
Bay of Rainbows
) a semicircular dark plain in the second quadrant of the face of the moon.