Noah Webster's Dictionary (n.) The quality or state of being tranquil; calmness; composure.

Multi-Version Concordance Tranquillity (2 Occurrences) Ecclesiastes 4:6 Better is an handful with quietness, than both the hands full with travail and vexation of spirit. (See NIV) Daniel 4:27 Wherefore, O king, let my counsel be acceptable unto thee, and break off thy sins by righteousness, and thine iniquities by shewing mercy to the poor; if it may be a lengthening of thy tranquillity. (KJV ASV DBY WBS RSV)