1. 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"
2. 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"