(of a body of water) free from disturbance by heavy waves "a lake of tranquil blue water reflecting a tranquil blue sky" - placid, quiet, still, smooth, unruffled
Not agitated; without losing self-possession "she became more tranquil"; "tranquil life in the country" - calm, unagitated, serene
See also: calm, composed, tranquility, tranquillity, tranquilly