Definition of "placid"

April advanced to May: a bright serene May it was; days of blue sky, placid sunshine, and soft western or southern gales filled up its duration.

1847, Charlotte Brontë, chapter 9, in Jane Eyre‎, HTML edition

The ant has made himself illustrious / Through constant industry industrious. / So what? / Would you be calm and placid / If you were full of formic acid?

1941, Ogden Nash, “The Ant”, in The Face is Familiar, Garden City Publishing Company, page 224

[I]n the 575 days since [Oscar] Pistorius shot dead his girlfriend Reeva Steenkamp, there has been an unseemly scramble to construct revisionist histories, to identify evidence beneath that placid exterior of a pugnacious, hair-trigger personality.

2014 October 21, Oliver Brown, “Oscar Pistorius jailed for five years – sport afforded no protection against his tragic fallibilities: Bladerunner's punishment for killing Reeva Steenkamp is but a frippery when set against the burden that her bereft parents, June and Barry, must carry ”, in The Daily Telegraph (Sport)‎