[adj] free from disturbance; "a ribbon of sand between the angry sea and the placid bay"; "the quiet waters of a lagoon"; "a lake of tranquil blue water reflecting a tranquil blue sky"; "a smooth channel crossing"; "scarcely a ripple on the still water"; "unruffled water"
[adj] characterized by absence of emotional agitation; "calm acceptance of the inevitable"; "remained serene in the midst of turbulence"; "a serene expression on her face"; "she became more tranquil"; "tranquil life in the country"