'Tranquil' in the Bible

And the peace of God [that peace which reassures the heart, that peace] which transcends all understanding, [that peace which] stands guard over your hearts and your minds in Christ Jesus [is yours].

for kings and all those who are in authority, so that we may lead a tranquil and quiet life in all godliness and dignity.

but the inner person of the heart, the lasting beauty of a gentle and tranquil spirit, which is precious in God's sight.