The adj placid has 3 senses (first 2 from tagged texts)
1. (2) 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")
3. easygoing, calm, placid -- (living without undue worry; taking life easy; "an easygoing man rarely stirred to anger"; "an air of placid sufficiency")