Jem said placidly, "We are going to give a note to Boo Radley."
It had been a placid week: I had minded Aunty; Jem had outgrown the treehouse, but helped Dill and me construct a new rope ladder for it; Dill had hit upon a foolproof plan to make Boo Radley come out at no cost to ourselves (place a trail of lemon drops from the back door to the front yard and he’d follow it, like an ant).
There are no more uses of "placid" in the book.
Show samples from other sources
a ribbon of sand between the angry sea and the placid bay
I scan their faces, trying to look as placid as possible.