|Noah Webster's Dictionary|
(a.) Quiet; calm; undisturbed; peaceful; not agitated; as, the atmosphere is tranquil; the condition of the country is tranquil.
Tranquil (2 Occurrences)
1 Timothy 2:2 for kings and all who are in high places; that we may lead a tranquil and quiet life in all godliness and reverence. (WEB WEY ASV DBY NAS)
Proverbs 14:30 A tranquil heart is the life of the flesh; But envy is the rottenness of the bones. (See JPS ASV NAS RSV)