Mare Tranquillitatis

[trang-kwil-i-tah-tis]

noun

(Sea of Tranquillity) a dark plain in the first quadrant of the face of the moon: about 110,000 sq. mi. (285,000 sq. km).

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