Mare Serenitatis

[suh-ren-i-tah-tis]
noun
  1. (Sea of Serenity) a dark plain in the first quadrant of the face of the moon: about 120,000 sq. mi. (310,000 sq. km).
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018