Sinus Iridum: Meaning and Definition of

Si•nus Ir•i•dum

Pronunciation: (sē'nus ir'i-dum, sī'-), [key]
  1. (Bay of Rainbows) a semicircular dark plain in the second quadrant of the face of the moon.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.