It was impossible but that Mrs Clay must hate the sight of Mr Elliot; and yet she could assume a most obliging, placid look, and appear quite satisfied with the curtailed license of devoting herself only half as much to Sir Walter as she would have done otherwise.
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.