Open English Wordnet
Adjectives
(s)placid, quiet, still, tranquil, smooth, unruffled(of a body of water) free from disturbance by heavy waves“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”
(s)equable, even-tempered, good-tempered, placidnot easily irritated“an equable temper”, “not everyone shared his placid temperament”, “remained placid despite the repeated delays”