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Meaning of Mare Tranquillitatis

Ma're Tran•quil•li•ta'tis

Pronunciation: (trang-kwil"i-tä'tis), [key]
  1. (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).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.