"placid" in the adjective sense
1. 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"
2. equable, even-tempered, good-tempered, placid
not easily irritated
"an equable temper"
"not everyone shared his placid temperament"
"remained placid despite the repeated delays"
Source: WordNet® (An amazing lexical database of English)
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